Mashups are a popular item these days, and it seems pretty much every franchise has at least a dozen or so to their name. That said, this one had not come my way yet, and I thought it deserved some love. Francesco Simioni has a fondness for both Final Fantasy and Street Fighter and so started a series of works mashing together characters from both. Featured above is my favorite, starring Chun-Li and Fang (of Final Fantasy XIII), but I've included some other entries down below. You can also find a few more at his Deviant Art page, and if you have any suggestions, make sure to send them his way.
So, what would your recommendations be? My picks would be a Red XIII mixed with Blanka, or a Wakka and DJ mix. Yeah, you didn't think I'd fit Wakka in there, but AH HA!