If your event has a decade theme—the sixties, the roaring 20s, etc.—crazyfads.com can help connect you to what was hot at that point in time. It's scary how well I remember some of the fads from early on in my life, especially my teenage years when fads were, like, so important. Everyone thinks of Saturday Night Fever and leisure suits when it comes to the seventies, but that decade also brought us Gee Your Hair Smells Terrific (check, had that), Earth shoes (loved those!), and string art (tried it and gave it up—too frustrating. Went back to macrame, which strangely doesn't make the list for the sixties or the seventies).
Anyway, there's lots there to spark some creative decade-based theme ideas. Thanks again to UNLV professor Patti Shock, who it appears is a fount of information when it comes to this kind of thing.