Looking for suggestions for keyboard upgrade

I currently have two keyboards:

A Yamaha PSR 630 and a Roland PC 200 MK 2 midi keyboard, neither of which are particularly good for live work.

I am looking at replacing these with one or two keyboards that would be OK for studio and live work. I would also like with better sounds (possibly from a tone generator etc.) 

Also, I wonder if a keyboard that could also connect to usb might be better for ease of using backing tracks etc. rather than using a CD player

I just wondered what other people were using and what you might recommend? 


Other gear:

EMU 1616 PCI, Sonar 8.5, Windows XP