Recommend your best sounding LP's

Cz- not sure how you play grade a sealed record, but I usually don’t buy old sealed records b/c there is often no recourse, and it is truly an unknown. PS: if you mean that a sealed record can have problems, I agree. Perhaps I misunderstood your point. 
regards,

mmporsche- congrats on your new table. (I had responded to your earlier thread about the point of diminishing returns by suggesting that it varies, depending on a lot of factors). So, too, with record recommendations: are you after "sonic porn" just to show off your system?--in that case, a lot of those old direct to disc records sound impressive, but at least to me, the music is "safe" if not banal--the equivalent of sonic wallpaper. Once you are open to adventure- and going beyond the audiophile warhorses, it is almost impossible to catalog the possibilities; much depends on your musical preferences--
and your willingness to explore material unknown to you. For me, some interesting finds (which were new to me, but maybe old news to others):

Crossings- early Herbie Hancock- spiritual jazz-interesting polyrhythms- U.S. pressing on Warner green label is wonderful. If you like this vein, there is a label called Strata-East that has a ton of extremely cool stuff--John Betsch Society-Earth Blossom; Heath Bros- Marchin’ On (especially the "Betty Suite"). The surfaces on these releases aren’t the best and they now fetch real money, but are worth exploring;

Prog Rock- I started to go beyond the usual suspects (ELP, YES, Crimson, etc) in several different directions- some of the Vertigo Swirls are amazing, but so are the prices- a US Swirl of Patto’s first album shouldn’t set you back much; if you are inclined to spend big money, both Cressida albums on Swirl are marvelous, keyboard centric jazzy prog rock. Though I hadn’t heard ELP’s "Pictures" since it was released, the first UK pressing, with a "Porky" inscription, will floor you. (Thanks, Ken Golden). Some of the deeper stuff from Italy and Germany is also fetching big bucks, but there are King Records reissues on the Seven Seas imprint from Japan that are cost effective and pretty good (better surfaces too, though not as vibrant sounding as the original pressings). If you want a taste of Swirls without spending crazy money, buy a UK pressing of the 1970 Vertigo Annual- it was a sampler, two record set with some of the uber cuts for cheap. (Gateway drug warning here- you may start spending money on the individual albums). Ken also turned me onto some of the RCA Neons, which were a continuation of the Vertigo approach on RCA- these get pricey but Indian Summer is not insanely priced as a UK pressing.

Hard Rock- Brian Davison’s every which way- U.S. Mercury- fantastic musically and sonically. He was the drummer for The Nice and the music reminds me of Traffic. Stunning audio- not expensive. Iron Maiden- The Number of the Beast- yeah, metal, but look for the Wally T. mastering on both sides- pretty spectacular if you like this stuff. Lucifer’s Friend- s/t- now considered "proto-metal" it is a Sabbath-y Zeppish record with Deep Purple-y organ fills and Heep style vocals (John Layton later sang for the Heep). The "one" is a German first press on Philips. Cool record. Dumb and obvious, but worth revisiting- Alice Cooper’s Love it to Death- but you have to find the early Straight label copies, before relabelled on Warner green. The difficulty here is condition. This is one of the great hard rock guitar albums, putting aside the whole schtick (which I thought was juvenile at the time - killer recording and some deranged playing).

Psych-Folk- The best known Fairport album Liege and Lief on UK Island pink label. Condition is key because there are a lot of soft passages- The two preceding releases--What We Did and Unhalfbricking are also worth the price of admission, which may be steep for the first pressings, but you can cheat. John Martyn- Solid Air- killer- also on Island; Roy Harper’s Stormcock- early UK Harvest- Jimmy Page plays guitar on at least one track- this album is a moody, dynamic and an extremely involving listen.

Gnu-ish stuff- I never thought I liked new "metal" but Opeth’s ’Damnation" re-released as a twofer with Deliverance is gorgeous- Damnation was remixed by Steve Wilson. This is natural voiced, less crunchy stuff and was my gateway into the band. Trixie Whitley- "I’d Rather go Blind" single EP from Belgium- not the one with multiple tracks-cut at 45 rpm, fantastic record, which leads you to Black Dub, and also to her late father, Chris Whitley- original pressings of Living with the Law, and Dirt Floor are worth seeking out. (The latter was only pressed by Classic Records, and one of the true obscurities on that reissue label--hard to find, but worth it just for the title song, recorded on a two track in a Vermont barn- a man and a guitar).

So many great records to explore- from standard issues- many of the Warner green labels from the era have both great music and great sonics. Usually cheap, too, in the States.
Welcome to the adventure of exploring "unknown to you" records- this is where the fun is ( and is hugely rewarding when you find something that ’clicks’). Any list is just skimming the surface here.

mm- no one source. Discogs is a decent starting place, but grading and pricing is all over the lot. For stuff like Warner green labels, many can be found in bins in used record stores all over the U.S. The Steve Hoffman forum is a good place to get a handle on some better known pressings of "classic rock"- just run a web search for "best vinyl pressing of X" (where X= band or artist or album title) and you'll probably wind up in one of the Hoffman threads. (Don't take anything on faith, but the better informed threads usually involve comparisons of different pressings, and rarely conclude that there is "one" best). I've gotten records from all over the world, and do rely on a few established dealers, but like many people buying used records, I also bid in on line auctions. You need to do your due diligence on pressings- some of the descriptions are not always accurate, and as I already mentioned, I tend to take grading with a grain of salt. (Visual grading tells you the record looks good, that's pretty much it-aside from play grading, which is also subjective, ask about warps). Part of the fun is the discovery, the research and the chase, rather than one stop shopping. 

Steve Wilson = genius. Multi-instrumental, mixes, produces, remixes famous classic prog, cool sounds, constantly cranking out stuff, different collaborations, including that Israeli rock musician, his stuff with Mikael Akerfeldt of Opeth. Guy can do it all. His remixes of Tull's Benefit and Aqualung were great, and dirt cheap on vinyl. 

@bdp24  very kind of you--I'm a piker compared to some collectors or musicologists, but retiring has given me the time to really dig down. You're no slouch either.
@goldeneraguy So nice to see you post. Always enjoy seeing you here- bringing a little humanity to the sterile environment of the Internet. 
(I've often found that people are different than you expect when you meet them in person compared to their Internet persona--usually to my pleasant surprise). Carry on! 

@fundsgon - even the old standard issue Warner of RLJ’s debut is pretty fab. (I don’t know how many different pressings of this record I have). Girl at Her Volcano, the EP, is pretty wonderful too (the digital aspect of this recording is not a negative even though early days)- what always puzzled me was how good Girl is, and how nasty sounding Pirates was--there the MoFi LP is definitely an improvement.
Loved her back in the day- saw her in the early years, the dark years, and when she busted her chains, at Radio City or the Carnegie (somehow, I think it was the latter). Haven’t heard her live in years- the production team and players for that debut are as good as it gets.