The JV1010 (which I use to own) has the session expansion board fitted as standard and this has a great acoustic piano sound- much better than then bank A JV piano sounds.

As mentioned above Yamaha S80 and P80 have superb piano sounds.

Check out Kurzweil K series and if looking at a Korg Triton- look at the piano expansion board- I own this and whilst it has recieved some criticism, I really like it!

The new Roland XV series (I've ordered an XV3080!) have great piano sounds- much better than JV series IMHO.

However, if you have access to a sampler than find a CD ROM you are happy with and load it in!