Bookman's is a Tucson institution and, quite frankly, the best used bookstore in town. There is great selection for books, DVDs, music and games. The staff is friendly and can help you find almost anything (with the exception of used textbooks-I haven't had much luck with those). Bookman's buys used books, music and movies and you can sell for either trade or cash. Trade is the better option in my book, you don't get much cash.
Bookman's also has a great kids section and is a family friendly place to shop