Just wanted to put a word in for this bit of software.
Basically even if you have a Behringer Guitar Link or one of the cheap ripoffs from Hong Kong, it will allow you to turn your laptop into a high powered and super versatile effects unit. Not only that but if you have a clean and comfy set of earphones, you can play along to your MP3 tracks and the amp modelling and eq options will allow you studio quality sound. The bass amp options are very limited (basically an Ampeg clone) but there are loads of screamy, grindy, tappy, wowy, zorky, echoey types of things and...at last...the kind of intuitively easy, logical, graphical user interface that multi effects units have been crying out for since the 80's.
I wasn't that impressed with the Ampeg sim, but the Fender Tweed and Bassman type sims were OK with guitar. I found bass was best with no amp sim but using a compressor and the parametric eq yields extremely nice sounding results. Being able to boost down as low as 30Hz delivered really satisfying B string sounds.
So this bit of kit has been soley responsible for me getting back into practicing every night and it sounds amazing. My ears never get tired and there's plenty to muck about with in terms of modifiers and such if I get bored. Plus the Kontrol USB foot controller means all I technically would need to do is take the laptop, controller, and a pair of IEMs to a gig. Crazy!
I think I've seen the future