These are pretty good, IMO. Granted, I do not use amp sims for heavy distortion so I've not tested these at extreme settings. But I can testify that, for clean sounds to moderate dirt, they're quite good.
And right in everybody's price range.
These were created by someone some of you will know, Dave Clark, who, with Ken McLaren, previously gave us the popular HeadCase and others. He's spent years perfecting the triode emulation code that's at the heart of these plugins. Accuracy comes at a price, though, and like all high-end sims these place a bit of a demand on your CPU. Not enough to be a show-stopper, but I wouldn't stick 10 instances in a project.
While you're there, you might want to check out the other freebies which include an EQ and a convolution reverb.
All are 64-bit Windows only.