I imagine some of you have heard of this, but it looks like some pretty nice modeling software:

http://www.scuffhamamps.com/

There are only three amps, and they're designed by the software author (not intended as carbon-copy models), but they sound pretty good to me and supposedly have pretty good IRs. Best of all, it's only $75. When I someday unearth my computer from storage, I might buy this.

One thing I noticed from the youtube demo below is that it seems to model the entire amp, not just one channel or setting or something. I imagine some of the newer modeling software out there does this as well, but I've only ever really used the Fender Fuse and Line 6 POD Farm. Those only seem to model, for instance, the extreme end of a Dual Rectifier, so you get the famous sound, but not the entire amp.

Anyway, check it out. They have some good clips on the website.