Political Commercials Since 1952 Online
A great site for political junkies with broadband...The Living Room Candidate is an online exhibition by the American Museum of the Moving Image. You can watch every single presidential campaign ad ever...I think. Doesn't appear that they are keeping track of every 527 ad...but hey, nobody's perfect. It's quite a walk through American history.
My personal favorite...The Ike Jingle from 1952 (also happens to be the first presidential campaign ad EVER...)