For organs I love the Creamware B-2003 (DSP based), but I assume you are looking for native solutions? NI recently updated their B4 to v2.0, adding some extra cabinet options for the Leslie sim and some refined tube distortion algorithms (I think). I don't own the B4, but I have used it several times and if this new version is improved, I think B4 2.0 will be as good as it gets natively (as far as not using samples).
You also might want to investigate NuBiLE, a very fairly (under)priced donation-ware organ VSTi (there is a free version, and a newer version that costs something like $30 if I remember right). This one actually sounds great, on par with the B4 I would say. It doesn't strive to emulate the Hammond B3 directly though, so if you are looking for a straight B3 emu, your best bet may be the NI B4. You can find info on this @ kvraudio.com.
As far as pianos go, I guess it depends on what flavor you prefer. I have the Vintaudio Yamaha C7 Grand set, and I love the sound of it. It comes with a standup Steinway piano that has lots of character too. The PMI Bosendorfer sample set is supposedly wonderful, but I have never tried it. Then there is the Malmsjo piano by ArtVista which has a very subdued and warm beautiful sound. This one is much cheaper than most of the VST sampler style pianos and has a great sound, although it would not work well for rock or modern ballads where a brighter sound is required.
I'm still searching for a good strings VST/sampler...Garritan and the VSL libraries seem to be highly regarded, as are the Miroslav libraries. Good luck in your search!
