As an organist, Leslie emulation is a big deal to me so I've tried just about everything out there. For live playing, I use a stompbox called a Neo Instruments Ventilator, which is by far the most accurate sim I've found.
 
But for computer-based effects, that title goes to the Leslie emulator in VB3. For 50 bucks you don't just get the world's greatest faux-Hammond on a computer, it also comes with a separate DLL that's just the effects portion.

IIRC, the VB3 fx plug-in is 32bit only. The synth is 32 or 64bit.

The Ventilator - If they made this pedal as a plugin I would buy it in a heartbeat. My last two keyboard players used this pedal for their national tours...Not only does it give you the rotary sound, it also
makes your tone sound bigger...They are not cheap however...
 
http://www.neo-instruments.de/en/ventilator/ventilator-features

I am really liking the new leslie gui in Amplitube 4! Although, I have been using the VB3 plugin and sometimes the older Native Instruments B4. I must mention when I was in 32 bit I used the freebies Mr. Mcdonald and Spinner Le. They yielded pretty good results depending on the mix.