I hope on recommedations on ($800-1800) polite/(thin) sounding bookshelves. Many miles away from sounding bloated. Easy, maybe a tad 'boring' and musical bookshelves. I'm aware that some wave this off as anti-hifi. But that's simply my taste. I want to enjoy them but not feel 'impressed' or overwhelmed by them.
I hope on some pointers on the right direction.
I think Ikea makes some decent sounding bookshelves?
British speakers tend to have the rep of being "polite" ... look for some of the LS3/5a models from Spendor, Harbeth or Clements ... older but still relevant and hold there resale value better than most should you not like them for some reason
Make sure that they don't have a rear port.
You could even go for something little in a sealed enclosure like gallo's with a sub on the floor somewhere?
LS3/5A's embody the soul of your request. They don't get better than this, that is why they are still popular 30 years latter! I've been responsible for a lot of friends buying them over the years, and most still have them, and just love them. BTW, I think the Rogers and Spendors were best at what you are looking for. Some of the latter ones started to 'enhance' the FR and some actually use different drivers, they are really nothing more than LS3/5a look alikes, not sound alikes.
Of course you must use front ported speakers. I agree LS3 is the way to go.
I'm a bit confused by the LS3/5a suggestion. While they are small and would fit on a bookshelf, the OP asked for a "thin" sounding speaker. I'd consider the LS3/5a to have anything but a "thin" sound. I've always found them to have a rather rich, textured and articulate sound, though absent deep bass due to their size.

That said, I do love the speakers (I have two pair of other model Spendors plus LS3/5a clones) and do consider them extremely musical, especially if one is fond of music primarily played on acoustic instruments and with unprocessed vocals.

Perhaps the OP could elucidate a bit more about the type of music he prefers and his volume requirements. In re-reading his original post, I'm not quite sure what I'd suggest at this point.
It seems like you are asking for a neutral speaker more than anything else, with perhaps more emphasis on detail than bass or midrange warmth, and not being annoying in the treble? I'd look at the Polk monitor 40's, which are very dry but enjoyable, and retail for about 2-300. If you want to spend more money as you suggest, the Aerial model 5's may be a good choice.
Thanks for the feedback so far! This is the first time that I looked into the Ls3/5a. It sound like a near perfect speaker.
I have a question for Newbee or anyone else who has experience with LS3/5a speakers (jrinterptnet?). Actually a load of questions:

mentioned are the splendor and rogers Ls3/5a as great speakers. What about Chartwell, Audiomaster and Harbeth?

I've seen a Harbeth Ls3/5a 1978 for sale for approximately $1300. is this a fair price? Sounds ridiculously high.

Wich speakers 20-30 years in use I would suggest that the cones are toast by now. True or false?

15/11 ohms. and inpedance of 84. Are they easy to drive or the opposite?

And my biggest concern is with the mid bass hump. I read that this is an issue with the Ls3/5a. Also true or false? The latter is what could stop me from purchasing a pair, so that's very relevant.

Thanks a lot guys!

The LS3/5a was designed by the BBC as a monitoring speaker for use in mobile recording vans. As such it is highly prized for its eerie vocal qualities.

They were manufactured under license from the BBC by a number of different speaker companies but they were all required to meet rigid specs. That said, there is a debate among audiophiles as to which is the "best" version.

The 15 ohm is the older version. Both versions use KEF drivers for both woofer/mid and tweeter. The crossovers had to be changed when KEF slightly changed the design of the woofer and the speaker went to the 11 ohm version. The speaker is fairly inefficient and will not play loudly, It is not recommended for anyone who listens above 90 dB or so.

$1,300 is a typical price and may even be a bit on the low side.

The cones are not "toast" due to age. They did not use the typical foam surround and do not deteriorate in the manner as some speakers. I've got a pair of "clones" that use the same drivers I bought while living in England in 1979. They play fine. There are replacement drivers available on the used market if you need one. One word of caution, though. The KEF drivers used in the LS3/5a were to a tighter spec than ordinary production run drivers so a replacement driver may not perform as precisely. (However, a working speaker is still better than a non-working one.)

There are some specialty web pages on this speaker and a Yahoo discussion group devoted to all things LS3/5a. You might wish to check them out.

However, I am still concerned about your original request for a "thin" sounding speaker. The LS3/5a is anything but "thin."

Here's a little bit of history about the LS3/5a from an Enjoy the Music review of the Gini LS3/5a. One thing they do mention is that the LS3/5a is a "monitor speaker" and not a "bookshelf speaker".

"Surely it must come to pass that in every audiophile life there is a moment of regret, something you would undo if you could. For me that moment was the day I sold my Chartwell LS3/5A Speakers. Now as I look back, it is 31 years since the speakers were first produced in 1975. The first American report I could find was back in March 1977 when J. Gordon Holt reviewed a BBC pair that at the time retailed for $430. The initial production run was small and only meant to fit a very specific need at the time. But that ended when audiophiles discovered the wonderful musical qualities inherent in this LS3/5a specification. Very few speakers have retained such a loyal following over so many years. If you do a web search as I did you might find an LS3/5a chat room. Looking through this site I found a British member reporting that in April of 2005 a pair of Chartwell LS3/5a speakers went for the U.S. equivalent of $2,500 on an e-Bay auction. The speakers have garnered a cult status very much like the acclaimed Marantz 9 amplifiers and Quad 57 electrostatic speakers. Production eventually came to a halt in 1998 when KEF ceased production of the T27 tweeter and the B110 midrange/woofer that was at the very heart of the design. This speaker is designated a Class 2 near field monitor and was developed after extensive research by the British Broadcasting Company (BBC) in the mid seventies.

The BBC had a need for a small monitor speaker that they could use in confined spaces like vans and control rooms. However this speaker is definitely not a bookshelf design. It should be placed well away from walls and placed on stands between 24" and 30" high when used in a domestic environment. It might not be widely known but there were actually two different versions that conformed to the BBC speaker specification. The initial production run manufactured a speaker with a 15 Ohm impedance and in later versions the speaker was a more compatible 11 Ohm load. The finalized 11 Ohm crossover was designated FL6/38 SP2128 and around 1987 both the crossover and drivers were supplied by KEF who started using computer aided matching. With KEF supplying both the drivers and the crossovers an ongoing problem with variability was largely resolved. Long time fans of this speaker will tell you that the later 11 Ohm version had a quicker more modern sound and that the 15 Ohm version had a more seductive vocal presentation.

A very important fact to keep in mind is that there never was any intention to design a totally neutral speaker with ruler flat response. The intention was and is to establish a standard and rigorously maintain control over all performance parameters. Having done that any LS3/5a speaker can be mixed or matched with any other LS3/5a speaker no matter when it was made and who may have manufactured it. Ultimately during the span of this 23-year production run they were produced under seven different licensed brand names they were in alphabetical order, the BBC, Chartwell, Goodmans, Harbeth, KEF, Rogers, and Spendor. I am discounting three other wannabe companies that failed or had little or no impact on production. With varying degrees of failure they were Audiomaster, RAM, and JPW. The Spendor speakers were I believe the second most prolific brand name associated with this product. The Spendor Company derived its name from the founders Spencer and Dorothy Huges. H.D. Harwood founded the Harbeth Company and another of the licensees was Richard Ross of Rogers. The combined output of these manufacturers ultimately totaled an astounding one hundred thousand pairs of LS3/5a speakers. One company in particular, the British company Rogers had a very long involvement with this project starting almost at the very beginning and I believe they account for the majority of the speakers now extant. The preceding narrative is only a very small portion of a very large book and even now the last chapter has not been written."

Btw, the Gini LS3/5a are modern and much more affordable speakers that attempts to "get" much of what was desired in the "classic" British manufactuered LS3/5a. But the fact still remains that IT IS NOT a "true" LS3/5a, although it does do a good job of capturing much of what is desired in a LS3/5a type of speaker.
Great history guys!

OP has asked about the bass bump. Here is my version of how you hear it. Boomy bass (down in the 60hz range) is not something the LS3/5a can do. The bump, as I recall centered somewhere around 125hz does add something to the speakers sense of warmth and imitates what a full range speaker might sound like so long as the actual musical information was not in the mid/deep bass. Keeps the speaker from sounding either cold or clinical as so many otherwise excellent speakers can when they start to roll off around 100hz. That is why I love these little devils...It is, IMHO, a great compromise. And no, they are not meant to be placed on a bookself, although some of my non-audiophile friends do and haven't complained. But I think you might hear the unwanted bass boost caused by close wall placement in these speakers, but perhaps most any others.

If you really do want a bass-less (so to speak) speaker there was one that has come on and off the market over the years - I'm trying to remember the guys name who designed it, but it escapes me. The speaker was I believe known as the Met 7. A remarkable little, sealed as I recall, speaker. I had a pair for some years and used them in a second system with a sub. They were not overly expensive. If that interests you perhaps a little reasearch would flush it out. BTW the manufacturer went on to make a SOTA tuner, if that would help in the search.

PS I just recalled - the designer/builder was Richard Sequerra. I pulled them up on Google when I asked for Met 7.
I have to agree with Misstl - 'the LS3/5a is anything but thin'.

But what a great little speaker it is!