I always love the sound of Korg or Roland keyboards. They program each different sound so accurately its as if you're playing the real thing. Plus action of the keys are somewhat similar to a grand piano .... i dunno how to say it ... erh, its like having a super cun Logitech keyboard, very "soft and nice to press" kinda feeling.

One tip, my keyboardist always said "If the keyboard is slim and sexy, its very expensive and sounds very nice" So if you come across a big, huge keyboard ... chances are its the low level models.