Simualanalog has a Fender sim and there's a Mesa Mark Sim afaik called Californian Sun or something like that.
Both are pretty nice for clean sounds, I am actually digging Lepou's HyBrit for cleans in the Plexi mode, too.
It's not a very modern clean sound, but it has lots of character, about free sim of an Ampeg SVT, I don't know
about anything like that, Ampeg SVX isn't free (but it sounds very good) the basspreamp (forgot who made it)
sounds very good and is versatile, TSE (onqel here) just released BOD, it's a tech21 bassdriver di simulation,
sounds great and especially in combination with the basspreamp and an ampeg cab impulse, you can get some
very SVT like sounds out of it.