Hi,
I have found the Digital Music Mentor software somewhat useful in the past.
DMM comes from Sienzo (
http://www.sienzo.com/) and it is a piece of software that helps you get the guitar chords and bass tabs for supposedly any pop, rock, blues or country song.
Basically all you do is load the program then pick a song from a CD or mp3 file and then click Analyze.
It's pretty simple to use and I found pretty good at figuring out chords, but the Key it thinks the song is in doesn't seem to be displayed right for the majority of the songs that I have used it on and the bass tab leaves a lot to be desired.
I have found it useful if I can't find or having trouble with working out and finding the chord structure of a song, but for anything else such as working out a bass line, it is by no means perfect.
Hope this helps though.
Cheers