These are by far my favorite happy YouTube videos. When I'm being a grump or annoyed with work, I just put one of these guys on and I feel better in no time.
Where the Hell is Matt?
I just recently discovered this and I'm obsessed. It's a lot better in HD, so if you have sec, mosey on over to YouTube and click on the little "watch in HD" button on the bottom right. Whether this is real or it's a hoax (which I don't think it is), this is definitely one of the greatest videos ever.
Schnappi Das Kleine Krokodil
As I post this video, I know everyone will finally realize how much of an odd duck I am. But this song/cartoon is just so cute. My brother showed this to me one day and I couldn't get the song out of my head for days, but I didn't mind. It's about a cute baby croc, what's not to love?