Finally, an iTunes Plug-In I'll use.

For those of us who never use the Visualizer in their iTunes, and sometimes like to see live music, I give you iConcertCal. (There are Windows and OS X versions)
It scans your iTunes for Artists, and shows you when they will be playing in your local venue (and you can change the venue with a click or two). Click on the show and it opens up your browser to a PollStar page to order tickets.
It crashed my iTunes a couple of times on install, and I think it's sort of kludge programming, but I think it's a very cool idea carried out sorta alright.
(Checking it again, and seeing that Pat Benatar is playing the Bergen Performing Arts Center makes me kinda sad, though.)