Quilt teacher Sharyn Craig (
http://www.sharyncraig.com/) addresses just this problem--what to do with blocks from swaps that maybe don't match in color or the sizes are a bit different, etc. She has a book (Setting Solutions) that talks about creative sashing to make these blocks work together. I went to see her at a guild meeting a couple of years ago--and she was just amazing!
Her book would be worth getting or see if your local library has a copy to check out--especially if you have lots and lots of "orphan blocks"...