I just bought the CMS Grandpiano 1 from cms sounddesign, a german company that makes really great samples.
It is installing right now, so i have not been able to try it yet, but if you are interested, i can record and send you a wave file with something i play.
The only thing, the sample size is almost 1gb, so you will fill up almost your whole flash module, unless you have a 2gb version.
I am happy to offer up the space, as i am really disappointed with the standard piano sounds, even other voices i tried from internet, such as the steinway voice from francesco massal.