Pick and Noodle - keep your eyes peeled on Computer Music magazine cover DVDs. At least once a year, they give away a fairly full featured version of one of the 'biggie' amp simulators.

Last year about this time they gave away Guitar Rig.

I've been using Amplitube LE for years with enjoyment.

Also shop your local Craigslist for Behringer V-Amp Pro units. Loads of great amp simulation and it will ALWAYS work with PG products, simply as an input into your soundcard (they have SPDIF outs if your card has SPDIF inputs).

-Scott