I LOVE THE KITTY CAT DANCE!!!!! There are some other flash movies on albinoblacksheep.com that are hilarious too. I recommend:
DooDooCaCa (kinda offesive if you're sensitive about race, but the music if funny)
End Of the World (MUST SEE, also kinda offensive with language)
Peanut Butter Banana Guy (classic)
Japanese Ping Pong (froma TV show, really cool)
STFU (this woman deserves the smack!)
When I need a good laugh, I go to ABS.com and watch these. Makes me chuckle every time.