I like downloadable from a "use" angle...
.WMV would probably be good for your bandwidth usage but touchy sometimes from what I've seen in quality.
What in my mind would be an 'ideal' customer minded arrangement is .mpg or .avi in smaller clips and larger ones too. Like 5-10 meg 1-2 minute in addition to like 50 meg clips too.
I don't much care for the monster clips like on those adultbouncer sites because downloading 200 megs just to see if you like something is counter productive.
But then again I'm an outcast in the industry so
-Dennis