EOS 5D Mark II, EOS 5D, EOS 50D, EOS 40D, EOS 30D, EOS 20D, EOS 500D, EOS 450D, EOS 400D, EOS 350D and EOS 1000D all have the ability to be powered from AA batteries when you use the Canon battery grips. The battery grips for these models come with a battery magazine that can be used with six AA batteries but AA batteries are not all equal. With battery grips costing about the same as a couple of Canon original batteries you might be tempted to try a battery grip and AA batteries instead of a pair of Canon batteries.
In practical trials of many of the listed cameras, using AA batteries is to be thought of as a 'get out of jail free card' rather than an everyday solution. If you forgot to charge your Canon batteries and need to shoot now, then the AA route can be a life saver. However AA batteries seem to only power the cameras for a very limited number of shots before their voltage drops and the dreaded low battery indicator and warning on the LCD show. There is some hope if you choose the AA battery route and that is Energizer Ultimate Lithium batteries. For some cameras they can provide longer shooting than a pair of Canon batteries in our trials, but they are not a cheap option.