I've tried alot of digital pianos, and I've yet to find one that can compare to even the unmaintained old upright in the garage, let alone to a Steinway D.

For the money, the Yamaha P series is pretty good. Anything with internal speakers will at least give you the above-mentioned vibration in the keys. Sometimes I play a P80 when I have to, and I don't totally hate the piano sound. I'm not sure about the p140, but I know they used a different set of samples when they replaced the p80 with the p90. The action is certainly better than any Roland or Korg.
The Clavinovas are great. More expensive than the P's, though. You'd probably do better to buy a real piano.
I'm not familiar with the GEM. The Yamaha beats the Korg hands down in terms of tone and touch (the Korg is kind of mushy).
I don't know of any sound modules that have better piano sounds than the Yamaha p's already have. If you are counting on using a module, and you are looking at a keyboard with internal speakers, make sure the keyboard has audio inputs... otherwise you'll need an external amplifier to use the module.