My husband discovered flash animation on the internet a couple of years ago. I have no idea how people make them, nor do I know where they find the time, but there are some really clever people out there (along with some really stupid people, of course).
But by far the funniest flash animation I have ever seen is
If you haven't yet have the pleasure of watching it, you have got to click on that link. Once it finishes loading, just click on Start. Warning: A little crude and not PC, but nothing horrible. If you dont' have the Macromedia Flash Player installed, it should prompt you. And make sure your volume is turned up (I turn mine off all the time).
For those who have or like cats:
I'm a Kitty Cat
The Laughing Cat
My favorite series of videos:
Neurotically Yours -- a series starring a goth girl and her crazy squirrel Foamy
And in honor of Star Wars Episode III:
The Star Wars Gangsta Rap. It's been around for a while, but it's great.
If you're interested in more ways to waste your time (not always PC, not always clean):
Albino Black Sheep