The Goodwill and Salvation Army here never have anything good. Best product I found at either has been Veronica Mars Season 2.
Now, Value Village is a different story. They get some real gems on occasion, but their TV series season sets (specifically the bigger thick ones) are usually $10-$15 at least and are heavily worn. They also have a problem with people stealing the discs (leaving the case empty) or putting a different disc in there.
On the other hand, I would have never known that 4Kids sold a DVD containing just 1 one episode (a Part 2 episode at that!) of G.I. Joe Sigma Six without them.