Flowtown has an awesome infographic on The Evolution of Geek. And I swear, it's like they looked at my high school year book picture to create the illustration for the D&D Geek.
Something I learned from their infographic is that geek is a variant of geck, a word from the 1500's indicating fool or simpleton. Wikipedia, of course, goes into a bit more detail:
The word geek is a slang term, with different meanings ranging from "a computer expert or enthusiast" to "a carnival performer who performs sensationally morbid or disgusting acts", with a general pejorative meaning of "a peculiar or otherwise dislikable person, esp[ecially] one who is perceived to be overly intellectual".
This word comes from English dialect geek, geck: fool, freak; from Low German geck, from Middle Low German. The root geck still survives in Dutch and Afrikaans gek: crazy, as well as someGerman dialects, and in the Alsatian word Gickeleshut: geek's hat, used in carnivals.
Formerly, in 18th century Austria-Hungary, Gecken were freaks shown by some circuses. In 19th century, in North-America, the term geek referred to a freak in circus side-shows. In some cases, its performance included biting the head off a live chicken. The 1976 edition of the American Heritage Dictionary included only the definition regarding geek shows.
So, any of these geeks resonate with you?