Here's a good song to practice your bar chords on: All Along The Watchtower. Many different artists have done versions of this song over the years. It's a pretty cool jam tune, so if you've got a friend who plays guitar as well (or bass), why not rope them into a jam session, and you can trade off on the rhythm and practice your improvising?
The chords for All Along The Watchtower basically go A - Bm - A - G, so the most challenging part is getting the rhythm right.
Any other songs you've always wanted to learn? Leave a comment below and let me know which ones they are!
Video Problems? Watch All Along The Watchtower on YouTube