Hi Tom
H264 in a QuickTime or MP4 wrapper, played on a flash player is what I would recommend. That's what we used when we developed our video review and approval application called ScreenLight. In fact, sounds like ScreenLight is something that may be ideal for your work-flow. Unlike YouTube, its brand-able (you can style screening rooms with your company logo and colors) and it's dead simple to accommodate end clients who don't want to spend time on anything with a steep learning curve. Like you said, they just want to click a button and watch. Anyway, it's free to try, and completely web based - so nothing to download. Check it out at
http://www.screenlight.tv
Richard Keating
Editor, Co-Creator of ScreenLight
"Centralized Video Project Collaboration"
http://www.screenlight.tv
Blog:
blog.screenlight.tv