The Nissin Di622 is a good gun for the money, reasonably well made and quite powerful, I sold a mint boxed one on here recently for £65 including postage. It will work in ETTL auto mode with Canon xxD models and xxxD models and also the 7D. It will not work with 1D series bodies for some reason. I do not know about the 5D and the 5D MkII.
It also has a built in slave, and will work off-camera but in this configuration it will only work in manual and you select the power setting.