Another rec for Blues You Can Use. For myself, the first book is too basic, but I really enjoy the second in the series, More Blues You Can Use, and the Jazzin' the Blues book is good too.
If you are interested in the jazzier side of blues, I would highly recommend the All Blues For Jazz Guitar series by Jim Ferguson. There are now five books in it, but the essential two are All Blues For Jazz Guitar, which teaches the rythm and comping side, and the All Blues Soloing for Jazz Guitar, which teaches soloing, obviously. Both are very well done, come with cd's, teach you the theory behind what you are doing, and are chock full of examples. I believe that they are still available on the Mel Bay website, or Amazon.com usually has them.
Out of the loop? I didn't know there was a loop!