I just bought NI Akoustic piano from eBay. It cost me £50 (even though it retails for £100). Unfortunately it's a discontinued product so it might be quite hard to find. I'm using it in the free Kontakt player in logic and its very nice indeed. Unfortunately it crashes a lot when run as a vst in mountain lion which is solved by running it in Kontakt.
Toontracks EZKeys for me. Depends on the sound you're after though. You can get some real classic grand, upright and electric piano sounds for EZKeys which all have individual velocity sensitive presets, but the more classic sounds still sound a bit electronic to be fair.
Honestly, Kontakt 5's Ragtime Piano mixed with True Pianos sounds amazing in my opinion.
With the right amount of EQ and reverb it can sound fantastic.