On the cat theme, I find this website hilarious
http://www.infinitecat.com/infinite/cat1.html
It started with a picture of a cat. Then someone took a picture of his cat looking at the picture of the cat. Then someone took a picture of his cat looking at the picture of the picture of the cat .... and it goes on and on and on (just click the next button).
For some reason, I laugh everytime I click the next button. Its so stupid, yet so funny.