Solo piano music. That includes both classical and contemporary new-agey type stuff like Jim Brickman and David Lanz.
I like Jim Brickman's style and his music, including his choice of covers, but after a while he gets pretty samey to me. David Lanz is a little better; he seems to break things up a bit more. But both of those guys keep things a little too safe for me in terms of chord choices and that kind of thing. If I feel like listening to New Age piano, I go with Liz Story or Suzanne Ciani. They both get just a little more adventurous and interesting, not afraid to throw in some wacky chords now and then.
Then there's good old George Winston. When he's hot, he can play circles around any of them.
Keith Jarrett goes even further, gets even crazier. Of course, at that point, it's full-on Jazz, not New Age. The Keith Jarrett Trio will blow your mind. Check out any vids of The Keith Jarrett Trio, with Jack DeJohnette and Gary Peacock, and prepare to have your mind blown.