These were all recced elsewhere--that's how I found them. So I'm just adding my endorsement to the pile. Hilarious, fuzzy, and cool.
Hilarious:
Things That Make You Go Hmmmmmm Sam is a jealous girlfriend. No, really. Oh, I laugh and laugh.
Fuzzy:
500 Miles It's SamnDean togetherness! Awww. I love this song, and it's wonderfully edited.
Cool:
Indiana Winchester Dean as Indiana Jones. It's so dang awesome it makes me want to cry.
Be sure to watch the YouTube ones in high quality, if you can.