I'm currently using a Hammond XM-1 connected to a Hughes & Kettner Rotosphere Mk2. It does a pretty decent job - the Rotosphere is supposed to be the best you can get without an actual rotary speaker.
For the Rhodes I am using the LearJeff soundfont running through FluidSynth on a laptop. Latency is decent but it has a tendency to stutter as the laptop isn't quite powerful enough. I'm looking at getting
a Korg Tr-61 or something for better orchestral sounds, so if it does a decent enough Rhodes or Wurlitzer I'll probably replace FluidSynth with that.
I have also used LoungeLizard 1 - which is nice, but I utterly loathe the copy protection scheme, since it will render the software useless if AAS should ever fold or discontinue it. I've also used '
Mr Tramp' as an alternative, but I'm trying to avoid softsynths unless I can get them to work outside of Windows.
For the mellotron I'm using the AKAI disk from
www.mellotron.com. The strings don't sound too good, choir makes up for it. The flutes tend to vary in pitch so they're okay (or not) depending on the music. This would probably be better with a truly AKAI-compatible playback engine that can use the 'retuned' program - I'm using some weird thing I designed myself.
If you've got a lot of cash, you might want to check out the Manikin
Memotron, which is a digital mellotron. It costs about a grand, though.