I just realized, while downloading the update for Perian 1.1, that I had never recommended it before: It calls itself the "swiss-army knife for QuickTime" and it has all the reasons to do so! Perian enables QuickTime application support for additional Media Types like FLV (used by YouTube) or HuffYUV, FFVHuff and other codecs you will never ever use in your entire life. But still, it opens Flash video in QuickTime and that is nowadays getting more and more important. So grab the newly updated Perian 1.1 here. Mac only, harrr.