Jean Michel-Jarre
Oxygene
but especially
Equinoxe(turn the lights off as well)
Anything by Kraftwerk
or Yello
Human League - Dare
Genesis - Seconds out
Electronic stuff seems to do well in the stereo separation game.
My two cents…
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Klaatu’s first album, sometimes called “2:47 PM EST”. The song Little Neutrino was built for headphones.
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Vangelis’ “Albedo 0.39”. Used a lot in Carl Sagan’s Cosmos series. In a dark room with phones on, man that’s good chicken.
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Robert Fripp’s “Exposure”. Who would have thought and album with both Daryl Hall and Peter Gabriel would be so cool. Terry Roche’s vocals on the title track still give me shivers.
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Queen’s “A Night at the Opera”. Prophet’s Song, 'nuff said.
and embarassingly…
- “Welcome to the Pleasuredome” by Frankie Goes to Hollywood. Way back when, a buddy with Stax headphones let me listen to this. It was a digital recording and just blew me away.
On a side note, do the albums that are great headphone albums also make great “crankin’ in the car when alone” discs, or are there different criteria involved.
One of my favorite CDs to listen to on 'phones when I worked out (back when I did work out…uugh) was Terence Trent D’Arby’s “Vibrator”.
He has a voice that seems like it’s made to be whispering in your ear, not blasting to a crowd.
NIN-Broken
Daft Punk-Homewerk
I second “Mezzanine”
The proof? Neo is listening to it on his headphones in the beginning of “The Matrix” 
Cyborgasm. It was made to be played on headphones, and damn if it doesn’t feel like a woman is breathing in your ear. (And it has a couple of tracks for the ladies too I think)