Well. Lots of stuff. He does full-blown manga, occasionally (see: NieA_7 manga, his contributions to Robot), as well as lots of independent doujinshi work (like White Rain or the Pochiyama stories). He's done character designs for several anime shows (including Serial Experiments Lain and Texhnolyze), and he's also done writing and directing for others (including Haibane-Renmei and NieA_7).
Also he just does art and design - lots of the doujins he releases are artbook/sketchbook type deals. His art is influenced by his experience with traditional Japanese painting, and he's got a fairly distinctive style, in part because he doesn't use a straight-edge in any of his drawings.
Aaand that's pretty much ABe in a nutshell. Cool art style, has worked on lots of pretty awesome and reasonably intellectual series. Unfortunately his (drawn, not animated) work isn't easy to get outside of Japan, but that's slowly changing, with nice people like DMP mirroring Wani's artbook/anthology releases in the US.