One of the things we have been collecting a lot more of recently at the Personal Computer Museum is ads.
I found this one interesting, as it shows Atari trying to promote the "business" side of things by talking about SynCalc, SynFile+, and SynTrend:
http://pcmuseum.ca/details.asp?id=41607&type=Brochure
I also like this one for the Epyx 500XJ joystick:
http://pcmuseum.ca/details.asp?id=39748&type=Brochure
And I loved the early LucasFilm games like The Eidolon
http://pcmuseum.ca/details.asp?id=37724&type=Brochure
It's also fun to look at company catalogs like Epyx:
http://pcmuseum.ca/details.asp?id=253&type=Brochure
What were YOUR favorite ads?