YouTube has an treasure trove of vintage soul video clips. Here's a selection:
Aretha Franklin - "Daydreaming"
Only the Queen of Soul could perform in front of a giant sign with her name on it!
Donny Hathaway - "The Ghetto"
Sadly only the middle portion of the song but well worth it to see Donny in action.
Stevie Wonder - "Don't You Worry Bout A Thing"
Everybody's got a thing, but some don't know how to handle it.
Otis Redding - "Try A Little Tenderness"
Gladys Knight & The Pips - "I Heard It Through The Grapevine"
Curtis Mayfield - "Superfly"
Al Green - "Love and Happiness"
(idea for this post stolen from Moistworks)
UPDATE: I had to add one more clip of Aretha singing "Don't Play That Song For Me." She just kills it.
More Aretha here, here, here here and here.