Canon 580EX II Speedlite, or just any big-ass flash?

Hi all.

I was working as a press photog last week and encountered a couple of situations where I pretty much needed a flash unit but didn't have one. Generally I despise flash, but I recognize that there are times and ways to use it to best advantage. I figure that most of the time I'm going to bounce it off the ceiling or otherwise diffuse it, and thus my question is whether I should buy the Canon unit (to use with a 5D or similar Canon SLR) or some equally powerful but less intelligent (and cheaper) one.

Thanks for any insight.