I like the Cheapo on Lake Street in Minneapolis that Jafox mentioned.
I've also had some decent luck at Half Price Books in St. Paul on Ford Pkwy. and in St. Louis Park on Excelsior Blvd. They have a few other locations throughout the metro area as well.
Discland in Bloomington on 98th and 35W has a decent stock, but I haven't really dug through their bins and checked it out for prices or selection.