I love these. Like most people youtube is my first port of call when I want to listen to a song online and it's great when there's more than an album cover on the video. Here are a few of my favs. Feel free to add/comment.

The classic viral vid
Bush and Blair at the gay bar.

A tale of life and death (of wolves)
Röyksopp - Alpha Male

A journey thru San Francisco circa 1910
Air - La Femme D'Argent

Okay this one's televised but Craig Ferguson miming to
Modern English - I Melt With You is v much in the spirit of home-made videos

As is this girl dancing to the Kaisers in a deserted car park
Kaiser Chiefs - Na Na Na Na Naa

And finally a collaboration of youtubers in one video
Junior Senior - Can I Get Get Get

I thought this home-made video for MGMT's "Kids" was pretty impressive:

http://www.youtube.com/watch?v=bIEOZCcaXzE

I love this one to "Stutter" by Maroon 5

http://www.youtube.com/watch?v=CmecMZ9o9rg

I love home-made music videos! There's so many I like that I'd be here all night posting the links.