Duke University has a digital library of vintage television commercials spanning some three decades, from the 1950s to the 1980s. The body of work in this collection includes ads for once-classic and now obscure brands like Super Bravo, Fluffo, Byrrh, Heart of Oats, Klean n Shine, Virex, Ansco and others, as well as brands still common today: Avis, Bounce, Charmin and something weird called Maxwell House.
You can browse the collection online and watch the commercials right in iTunes, and even subscribe to a specific brand and pull down every commercial they aired during those years. Check out Duke's AdViews. (Thanks Tara)