Duke University's AdViews Project has digitized thousands of 16mm television ads from the 1950s through the 1980s. And now you can watch them online for free! (As far as I can tell, you do need iTunes in order to watch them).
As bizarre as these ads seem (business men arguing over socks, women walking provocatively through huge flames to sell lipstick) it does make you wonder how far we've come in advertising. You can browse by brand (Watch out for Nucoa, pictured on the right. Their jingle is strangely hypnotic...), but I think the highlights are a good place to start. But be warned, the mix of sexual undertones, kitschy copy-writing, and cheesy animation makes for a deadly (but delightful) time-sucking combination!