I know that a few people used to use seven string guitars for jazz, and I'd like to know a few players and a few songs, as well as any weird tunings they used. If their are any blues players that used them I'd like to know about that as well.
Charlie Hunter - although, he doesn't use what you would think of when somebody says "7-string guitar." It actually has two bass strings (he also plays an 8-string with 3 bass)...look to fusion for anything outside-the-box like that, I'm sure there are tons of great players who use 'standard' 7-strings.