For sound alone, I have a Technics, I believe SX-PR603 or 703???, model number escapes me at the moment. Has some of the best sounds, full size 88 WEIGHTED keys. I can play Bach on a Steinway or Van Halen's "Jump" on an old 80s synth. I love this piano....
Other then that, I recently purchased an M-Audio Keystation Pro 88, it works great with the software I'm using, I can map most of the controls with the audio software (Native Instruments Anyone?) what can I say, I like to dubstep...
Only caviot on the Keystation.. bought it used on ebay and I think, or hope, there's a short in the rear USB plug. The piano appears to be disconnecting from my PC often. Sometime soon I need to take the whole thing apart and look for a cold solder joint.
Yeah forgot to mention, stand alone synths are great, but a good MIDI controller and the right software... It's Dynamo!