I like the quality of RM videos for the small size but I hate running real player cuz it tends to blast me with ads and install itself into my startup group every time (why do programs feel they are so important that I want them sitting in the background taking up valuable resources for the 95% of the time I am not using them?)

wmv is good but isn't it restricted to windows users? also if you are looking at any DRM I believe wmv is a requirement for most of these programs to work.

good old mpeg works best, its universal and can be played on any computer. You pay for that with slightly less quality and / or bigger file sizes but people almost never complain with an mpeg video on a paysite.

have you looked into divx? it produces high quality videos that are smaller in size, the only issue is that you have to point your users to the divx site to make sure they download the latest plug-ins.

cheers,
Luke