Yamaha has several items in the arena... The QY700, QY300 and QY70. The 700 and 300 are similar in price.
For the price - I would get the QS300 though. The QS300 is a keyboard version on the QY300 and has a very large following on the internet. (It costs about the same as the QY700.)
The difference I believe is that the 700 has 64 note polyphony and both 300s have 32 note polyphony.
The only real weakpoints is having to use an external program (XG-GOLD) to get the most out of editing patches.
Have fun.