The AudioAssault BlackSun guitar amp simulation, which runs on Linux (as well as Windows and Mac), is temporarily free (as in beer). I played with it this morning it's not bad. Quick to set up and comes with effects. As most of their plugins, it is a high gain amp. I dialed a very nice lead tone (although I loaded one of my own IRs with it), but did not have time to try a clean(er) tone at all yet.
Note that you probably need to provide your information to get it (like email). I had an account, since I bought some of their plugins.
I still prefer the tamgamp, but for a quick practice, the BlackSun works nicely and comes with effects already.
Just FYI...
AudioAssault BlackSun
Moderators: MattKingUSA, khz