Check out Steinberg's The Grand. Or Hypersonic 2 is hot.
I really do not recommend The Grand. It's really huge, but not worth the sound quality it presents. It is a lot better than a run of the mill soundfont or any other VSTi piano, but it's like almost 3 or 4 gigs (I can't remember) and it's a resource hog. I really recommend just using 4front piano mod and using effects on it very carefully. Reverb, chorus, and delay are your best friends.