I've got a Canon 580EXII which I use on my 60D and 5D3, and it is an excellent unit.
Powerful and controllable, and works perfectly with either camera and can be used a commander for multi-flash applications or as a slave with other 580's or the new 600.
However, they are expensive.
If you are getting into flash for the first time, I can highly recommend the Yongnuo YN560 or the 560-II.
The 560-II is a virtual clone of the Canon 580EX but it has one added feature, and that is that it can be used as an optical slave as well, whcih means no mucking about with the Canon system.
If it sees another flash go off, it goes off too, if you set it to do this, but it also works with the Canon wireless system and is one of the few aftermarket flashes that will work as a commander with other Canon or Yongnuo flashes.
The 560 and 560-II are the same unit, but the II has a rear LCD screen rather than just lights.
However, the plain 560 is probably easier to use for a novice.
You can get them from a forum sponsor,
Fotogenic for just $100 for the plain vanilla, or $130 for the II model.
Unbeatable value IMHO.
I'm going to get one too to supplement my other flashes.