I've heard the 750's are good cards for mining, but the 750 Ti's are currently the sweet spot with efficiency at scrypt/scrypt-n/x11 as well as a variety of other algos.
260Kh/s for a card that costs $100 (IIRC) is pretty good too though.
I recently got my hands on some of those, and oh boy, such a pleasure.
Cheap, quite, smooth performance. Can't even begin to compare them to my R9 290 rigs...