For reliability and flexibility, Sigma flashes are hard to beat. I've been using them for years, first with Canon, now with Nikon and am very pleased with them. Bag the cheap crap on evilBay and go with a known quantity.
I agree with Bob on this one. I have used sigma for a while. Good and cost less.
The question is not what you look at, but what you see.
- Henry Thoreau
I've used (and tested) the YN flashes -- unless you're going to be doing full-power pops continually for 20 minutes, you probably won't have any overheating issues. They're a very good bargain
I found a video, and they guy was firing the flash at full power until the flash stoped. The battery didn't overheat, the built in sensors stopped the flash to fire when it was 'hot'. I never did it to my canon flash, I may try sometime and see what is going to happen...