This is a tricky one. Canon's flash, the 430EXII would be ideal. But it is expensive. About $230 last I checked. I have a Sigma EX-610 Super that was only $135 and as much as I'm a big fan of their lenses, I'm not thrilled with the flash. It just isn't as reliable as I expect it should be. I don't plan to replace it because I don't use it too often and because I can usually chimp and reshoot if it blows out, fails to fire, or anything else weird. But if I were still shooting film for hire there is no way I would walk into a wedding reception with this unit.
A lot of people here have reported good results with the Yongnuo YN565 for about $130.
Metz and Sunpak make some decent units as does a company called Nissin. I would pretty much avoid any other names that I haven't mentioned here such as Polaroid, Vivitar, etc.
If you think you might go to multi-light wireless setups in the future, you may want to just stick with Canon.
I am serious....and don't call me Shirley.
Canon 7D and a bunch of other stuff