Director Thunderf00t has created a whole series of videos, dismantling creationist bull$#!t with surgical precision.
I know I’m going to cop flak for mentioning YouTube with their proprietary Flash-based system, so I’ll pre-empt you all. I’ve had mixed results with the likes of Gnash and Swfdec, but there’s always youtube-dl — a little Python script which downloads the underlying .flv file behind YouTube’s embedded-Flash movies. You can then play the .flv file using the ffplay command, which is part of the ffmpeg package. Just right-click on the download, select “save link as” and save it somewhere as “youtube-dl”. Type su followed by your root password to become root, then cp the file to /usr/bin/ and chmod +x it to make it executable.