ProjectM
I really like Notion (still on 5). And their iPad app is great too so notation is all over the place now ;)
I used to like Finaly a lot but it got a bit... "old" for me.
EDIT: I see they have something called Progression which seem to be aimed at guitarists
http://www.presonus.com/products/Progression
+1 for Notion. The only thing it won't do is a slide/bend from a ghost note, which I find irritating. I reported it N4, still the same in N5. I haven't upgraded to N6 yet, but prolly will at some point for S1/3 integration. G-Pro is OK, but kind of niggly to me. A new version has been announced for later this year. GP6 is ancient at this point.
FYI, Notion has everything Progression has plus more.