If your a guitarist your probably going to want Guitar Pro. Its a good piece of software for transcribing for all instruments and designed with the guitarist and tab lovers in mind. Its realistic sound engine also makes it a great tool for jamming along to a vast array of transcriptions available for free on the internet.
Another on for the guitarists but a FREE program that opens power tab and guitar pro files. A little basic on features but if your just looking for a more sophisticated way to learn some tracks from TAB then this is the program for you.
A well constructed and FREE piece of notation software. If you prefer notation programs like finale or sibelius but a bit strapped for cash then this is the program for you. Easy to use and overall a great piece of software.
The professionals score writing software. Lots of features and built for notating music. Can be sometimes a little tricky to master and comes with a large price tag. But there are some student and basic options available depending on your needs.