Best LPs to Test Turntables

I can recommend side 2 of Procul Harum's Shine On Brightly - "In Held Twas In I". A twenty-minute multi-section progrock suite!

I will add Quicksilver Messenger Service's Happy Trails - "Who Do You Love" - and the two instrumental tracks on side 2. Recorded live. John Cippolina was a phenomenal guitar player!

And not to be overlooked: "1983, Moon Turn The Tides ..." from Hendrix's Electric Ladyland. Along with "Burning Of The Midnight Lamp". Jimi at his psychedelic best!

I use a couple of 60s Columbia LPs that I am very familiar with:

Stravinsky conducts Rite of Spring, Columbia Symphony (really the New York Phil, but contractual limitations...)
- a truck drives by the hotel where they recorded, at a quiet moment on the first side. Prince Igor also stomps his foot during the Game of Rape (I think). It still makes me think someone is kicking my porch...

Bernstein conducts Bartok Music For Strings, Percussion and Celesta, New York Philharmonic, Columbia
- in the stereophonically-written second movement, Lenny quietly mutters "one, two, three!" under his breath, desperately trying to keep his two string orchestras together in one of the more treacherous multi-meter passages. I listen to see how much resolution the turntable/cartridge is capable of...

The Sheffield Labs Prokofiev Romeo and Juliet, that someone above recommended, is indeed an amazing disc, but I think it would sound decent on an average table. But it is a dry recording, so it would be interesting to use to see if the dryness is attractive or not.

I also have an old 1969 pressing of Arthur by the Kinks. It is fairly worn, so I use it to see how fine a stylus is, if it can retrieve grooves under the scratches. Benz MC carts win here. But you are testing tables, not carts...

Bring your best sounding uncompressed ones that you have listened to & know

I would bring:
Wilson Audio or MFSL pressings
Pink Floyd DSOM & The Wall 
The Damned -  Black Album, Anything
Clannad - in concert
Red Nichols - Marineland
Isaac Hayes - Hot Buttered Soul
Verdi - Requiem
Taj Mahal - Recycling the Blues

I would also bring my Portuguese pressing of Joy Division Still...