PezTab
 

My friend Pez is currently in the process of making his own tab program, using real guitar/bass/drum samples, which means you can have any instrument you want provided you have the samples!

He has a site - http://peztab.150m.com, where you can download a beta version of it, there'll be add-on packs too, such as a speed builder for all you speed freak guitarists :P

Check it out! :)

Pez chucked me a couple of the Beta versions for feedback, and it looked very promising.