Actually, anything by Rostropovich.
But the Dvorak Cello Concerto is a personal favorite of mine, and his performance of it is stunning.
Rostropovich's complete recording of the Bach cello sonatos also sublime. Yo Yo Ma's is also very good (not sure if Yo Yo has recorded all of them, but I know he's done some, and they're beautiful).
Yo Yo Ma also did a series of videos of him playing Bach Sonatas while some Japanese dancer guy dances some kind of modernistic kind of dance. Those are quite wonderful.
For some real mind-bending cello - especially since you mentioned you like slow stuff - check out Zoe Keating. She does a kind of minimalist/trance/psychadelic cello thing with loops and effects that's actually quite beautiful, and not just electronic tom foolery self-congratulatory masturbation. You can hear her on WNYC's Radiolab here:
http://blogs.wnyc.org/radiolab/2008/08/25/quantum-cello/Speaking of which, you should also always listen to Radiolab.