Also check out Revalver MKII. I played around with the demo but didn't give it enough time.
Features:
ReValver Mk II adds features like:
Truly advanced valve modeling, with amps and stomp boxes inspired from the original schematics.
Impulse Response speaker modeling, with hundreds of sampled speakers and cabinets.
Cabinet stress and speaker distortion.
Power amp rectifiers and output transformers.
Import or export your own Impulse Response files.
VST host module, allows you to insert your favorite VST plug-in right in the ReValver Mk II chain.
Fully MIDI mappable.
Yes you can insert other VST's right into the signal chain! Very cool!
http://www.alienconnections.com/products_revalverii.htm