Alrighty the little I know about triton/motif/fantom:
Motif is good for EP sounds... rhodes, wurly, clav, organs. Not so hot on strings/pads/synth. I tried the EP sounds on these, very nice. Didn't get to the other sounds, so that's all heresay
Korg (triton, M3, etc.) good for strings/pads, brass/woodwinds maybe? not so hot on EP sounds and piano sounds. This is all heresay, never played one.
Fantom good for strings and pads, and apparently not brass/woodwinds. A friend of mine uses a Fantom for dream-theatre like playing, and I borrowed it for some jazz stuff... baaad EP sounds. Personally I'm not crazy about the piano sound on it either. There's a lot of customization (how open the piano lid is), but the actual sound wasn't great. Could've been the amp, but there you have that.
Alright so the stage piano recommendation eh? I got to try a Nord Stage at a store briefly... gotta say the piano sound on there impressed me, since everyone seems to bash it. Wurly/clav sounds are nice, organ is nice. Didn't get to try the synth (don't know anything about them so didn't know what to do). Kanthos would be able to tell you more, but it might be worthwile. Overpriced IMO.
Yamaha CP-33 I tried in a store for a bit... decent action, didn't like the piano sounds (I'm not a fan of yamaha acoustic pianos either), though a lot of people do so might wanna check it out, of only for the action.
Another thing to consider, for purely piano sounds, is the GEM RP-X sound module
http://keyboards-midi.musiciansfrien...ule?sku=702865 hooked up to some keyboard (CP-33) or midi controller with an action you like, possibly something by studiologic.
http://keyboards-midi.musiciansfrien...ard?sku=700737
http://keyboards-midi.musiciansfrien...ler?sku=708348
I believe the studiologic controllers (specifically the VMK, not sure about the SL) have the same action as the Nord Stage, if this is the case I would recommend it (they are both Fatar actions I think).
I bought a Roland RD-300sx 8 months ago... I initially liked the piano sound in it quite a bit, and through headphones they're ok, but I always end up going to the EP sounds on it. Basically... keyboards do not sound like pianos. They're somewhat close, but unless the GEM RP-X is mind-blowing, I haven't heard a keyboard that sounds close enough to my tastes. Still doesn't respond and act like a piano. There's some good software out there like pianoteq and ivory and things like that I haven't checked out, but on-board sounds on stage pianos I'm not crazy about.
For action as well I'm not crazy about hammer-action (and I've played nothing but acoustic for 18 years). None of the ones I've played, Yamaha cp300 (this was admittedly the best one), Roland RD-700gx (decent, overrated IMO), feel like an actual piano. I'm actually likely going to buy a motif rack and a semi-weighted controller soon and go that route. Depends on your needs I suppose.
Personally if I wanted a keyboard that sounded as close to a piano as possible, I'd be inclined to get a GEM RP-X sound module with a controller (I'd either try it out first or just return it if it sucked). The cool thing about that option is it costs just about the same as buying a Yamaha CP-33 but there's a lot more piano samples and editing options (I believe anyway). My knowledge of that comes from other forums where a lot of professional keyboardists post. Take it for what it's worth.