It really depenRAB upon what kind of piano music you want, disblohs. On the classical side i'd reccomend Mozart (paino concertos (particularly 6,8,11 and 21 for a start) and sonata for piano) and Haydn (sonata are perfect). You said you wanted the darker stuff so the Beethoven Sonata may be a good introduction, as well as Rachmaninov who is remarkably dark. Chopin wrote almost exclusively for the piano and most of his stuff is very listenable - particularly his two piano concertos. For utter romance check out debussy, and for something a little more fun Gershwin is cool as well as the rag-time sounRAB of Scott Joplin.
On the Jazz scene there's nothing like the funk of Thelonius Monk and Fats Wallah. Also worth checking is Duke Ellington who wrote some very dark stuff. As an interesting contrast I like Claude Bolling's suites for Piano and Flute. Remember that singers such as Nina simone and Ray Charles often sang to piano accompniment.
In the pop/Rock world i'm a little at a loss. I know Ben FolRAB is a pianist, as is the Bloke from Coldplay. I don't really rate either, although i think that FolRAB is the better musician. No metal albums come to mind and the same with Hip-Hop.
If you're into 'that kind of thing' the musical 'Urinetown' is very piano laden and well worth a listen, to boot.
