Recommendations for bookshelf speakers

I hope some of you knowledgeable folks can help point me in the right direction here. I've just sold off a pair of venerable old Celestion SL600s to a friend who's setting up her own system. I've been using these for casual listening, mostly as computer monitors (YouTube mainly, and some streaming broadcast services, with very occasional forays into higher-res formats) and as musical as they are, I think it's time for something more modern and more efficient.

Well, this is where I get lost. I'd like something that approximates the Celestions' musicality, but scouring the internet for information on speakers of appropriate size and price (I can go up to about $1000 for these) just seems to muddy the waters. I'm happy to go with either used or new. A few that I've looked into but been put off by various aspects of their reviews: Monitor Audio Silver 50 and RX1, Polk Audio LSiM703 (there's a really good deal on these on Polk's website, but they're quite a bit bigger than I'd like), various models of Elac's bookshelf speakers, PSB Imagine Bs, and even a few used B&Ws, a brand I've never really liked all that much.

I'd be grateful for any suggestions you might have. There's an endless variety of speakers out there and I feel I've barely scratched the surface. Your suggestions would be gratefully received. Thanks!
I haven't heard a pair yet, but the Klipsch RP600-M sounds like it might be a real killer at $550/pair. You can use low powered tube or solid state amps with them as they are very efficient and high sensitivity.

The RP-600M is indeed a great speaker for the price; however it’s impedance in the treble is very high, thus a tube amp would make the speaker sound brighter, and it’s already bright to begin width.

Despite popular belief, Klipsch speakers aren’t actually that high sensitivity (par the Heresy and such). Klipsch states sensitivity as in-room and not anechoic, historically they use +6dB. So even though the RP-600M states 96dB, it’s actually 90dB (John Atkinson estimated it at 89.6dB). Still higher than average, from a far cry from the ridiculous 96dB spec.
The KEF Q350's are a really fun speaker - I couldn't personally live with the LS50 but the Q350 have really good boogie factor going for them.

There are a pair of B&W's that go for a bit more that are also supposed to be really good bookshelves not sure which model but probably still in budget.
The Polk 703 are very nice. I had the Lsim705 but they were too big for my office so I sold them. The 703 weigh about 30lbs each and are built very well.
There's an endless variety of speakers out there cooper......You didn't mention what electronics you will be using to drive the speakers. A most important element. If you have the opportunity to audition speakers with YOUR electronics that would be a big plus in your decision. Some speakers sound great with some electronics and not so good with others.
Your statement..... "There's an endless variety of speakers out there" is so true. You will receive countless recommendations from many who have different speakers and attest to their satisfaction with their speaker choices. Most opinions will be base on complete system setups and personal tastes. Audition speakers if you can!!
I have a pair of Celestion SL700s (stand mounted) in my bedroom. I don't plan to part with them. Ever.

That said, you should always audition speakers - and preferably at home and in situ. If your budgets can handle it, you should consider a pair of LS35a. Even today and almost regardless of the manufacturer, they represent a landmark speaker.
I've mentioned these speakers it goes...wharfedale diamond 225's. They have to be heard to be believed, for just $449 I don't think they can be beat for an honest sounding audiophile speaker. A touch of warmth, non fatiguing, unbelievable bass response, crystal clear highs, and a sweet midrange. Stereophile recomended component. 
Parts Connexion has Wharferdale and Monito Audio on great discounts right now. :)

If you go wiht Wharferdale, highly recommend a cap upgrade. Totally worth spending $40 on a pair to upgrade them.
I don’t see where you mentioned your equipment setup.  I am really enjoying my ELAC Debut 6.2 bookshelf speakers with my CA Topaz SR20/ NAD 7020 and Linn Axis turntable.  
I recently bought a pair of JL Labs Focal Aria 906 speakers and I really like the sound I'm getting. They are efficient and if you look you can get them for well under $1,000. They did take some time to break in though.
My last system was with Vandersteen 3A signatures, Aragon 8008BB power amp & Adcom GFP-750 Preamp. Current system is Maggie 1.7is, PS Audio Direcstream DAC & PS Audio BHK 250 amp.  My bedroom system is a Nuforce STA 200 power amp with a pair of Focal 706s. These are amazing speakers & I got them for $450 a pair new here on Audiogon from  Canadian dealer. I have not heard ANYTHING remotely this good up to $800. I chuckle every time I hear them. Punchy, clear, revealing, delicate, open & with good imaging.  No brainers at $450.
My favorite bookshelf speakers right now are the Focal 906. I have used them as near field listening monitors for PC, as L/R paired with a PS Audio Sprout 100 in a 2 channel configuration, and as Surround L/R in an all Focal 5.1 configuration with a Yamaha RX-A1060 AVR.  I have never been disappointed, in fact they rival their tower big brother - the Focal Aria 926. I am positive you can pick up a pair of 906’s in your budget, either new on sale or gently used here on Audiogon. Happy hunting! 
For the money the ELAC UniFi UB-5 speakers are great. They are also just very good speakers. An added bonus is that for some reason, they are heavily discounted and you can find them on Amazon. If you want to move up to they big brother towers the ELAC UniFi UF-5 are even better and discounted too and on Amazon. These aren’t bookshelf or speaker stand speakers in the traditional sense, but the Magnepan Little Ribbon Speakers (LRS) are excellent, and ordered directly from Magnepan for only $650!
I bought the SVS Ultra bookshelf speakers about a year ago. They are fantastic. Silky smooth, tight bass. I’d check them out for sure. Good luck.
Thanks for all your suggestions. There are a few speakers presently listed here on A'gon that I'm very interested in: Some Spendor SP 3/1Ps and the above mentioned Focal Aria 906s. From this you might get an idea of what appeals to my taste. Speakers like the KEFs (and a lot of other modern speakers I've heard) are clean and tight with great imaging, but I find them uninvolving, sometimes downright shrill. I'm also interested in LSA .5s but I haven't seen these for sale anywhere recently. Discontinued, I think. 

A bit more detail about my system: amplification is an Arcam A85 integrated, and between the computer and the amp I'm using a Musical Fidelity VDac II (basic but very serviceable DAC). Digital optical cable between computer's sound card (Soundblaster Z) and DAC.  

I doubt that you would go wrong with the Spendor 3/1p. I’ve never owned a Spendor that I did not like!
Just a quick question for the Spendor owners, if you've heard both of these: considering their English DNA,  I'm wondering how these speakers compare to Harbeths. I'm not a fan of the latter, as I feel they err too much on the "warm and fuzzy" side. Thanks.
I personally would not screw  around with The wharfedale speakers, to me they sound terrific just the way they were designed. I like to leave the sound signature to the designer, as I'm not one. 
Update: I've settled on a set of Focal 906s (new) that were listed here on A'gon at an irresistible price. They'll be here tomorrow. It'll take some time for them to find their voice (100 hrs. or so, I'm told) but I'm really looking forward to hearing them. I'll let you know what I think when I've had a chance to put them through their paces.
Thanks again for all your suggestions.
Hey OP,
Focals, like Wharferdales, benefit greatly from cap upgrades. With Focals, I find replacing the tweeter caps with Mundorf MKP to be a really smooth sounding upgrade, and really inexpensive.

Best of luck,

Congrats on the Focals, Cooper. Definitely let us know how you like them.
Unlike tower speakers, bookshelf-size speakers are so easily transported that there’s really no reason not to buy and try. Since it’s easy enough to sell the ones that don’t work for you.
Focals arrived today and they're playing happily away in my system. Right out of the box I'm impressed with their remarkable imaging and facility with vocal tracks. I thought a good touchstone would be a CD of Bach's St. Matthew Passion, where the opening chorale features a double-choir. Wow. The sense of space comes through in blazing technicolor.
Because the speakers are still brand-spanking new, they sound kind of closed up and overly polite but I'm sure this will all open up with sufficient playing. It's really unfair to try to assess them right now, because they obviously need quite a few more hours of break-in before I can get a true sense of what they're capable of, but I'm looking forward to hearing what happens as they open up in the coming days. Well weeks, more like...
Update: the Focals have had their requisite 100 hrs. of break-in now and I do think they've opened up rather nicely.  This difference isn't anywhere near as dramatic as what I experienced with the new pair of ProAc Response 1SCs I bought a good few years ago. Now, THAT was a learning experience!

The Focals' stereo imaging is truly excellent and their presentation is musical and involving. No, they don't dig very deeply into the bass but the sound is nicely balanced all the way up the spectrum and my typical listening levels don't extend to floor-shaking low frequencies anyway. Just for fun I tried these out in my main system (Modwright KWI 200 amp, Cambridge Audio CXU, AMR DPP 777 DAC, Rel S-2 sub) and though they were no match for my Ryan R610s, the things these Focals did well they did very well indeed. Don't drive them too hard though, they'll get kind of harsh. But for the way I'm using them, they give me exactly what I want to hear, so I'm sure they'll be sticking around for a good few years.

Once again, thanks to all for your opinions and recommendations.