We'd like to hear detailed descriptions of problems viewing videos in standalone players and browsers. HTML5 and WebM especially are very new, and it's highly unlikely the experience in any browser is going to be free of hiccups quite yet. The more feedback we get about what doesn't work, the more we can do to make sure problems get fixed.
If you don't see your browser or player below, feel free to add it to the appropriate list. And to avoid any battles over natural pecking order, keep them in alphabetical order ;-)