I was thinking of the logo as the website name "masteringapi" with a character (geek) holding a wrench (representing "web service" or "web api") next to it.
Maybe the character would be like one of the mangatar (or faceyourmanga) style with huge head, thick glasses, light beard and small body.
I do like black/white templates/themes (black on white), just like my website. So I prefer using these colors for the wording "MasteringAPI", but I don't mind the character to have some colors (but not too flashy).
P.S.: while the character might be attached to the wording (masteringapi) I'm planning to use it as a "profile" for me on Stackoverflow and other communities. So something on the shirt like (M.API) would be great (or something like big M, superman-like), also this means when the winner deliver the design the character should have a standalone layer to export it as described.
UPDATE: In addition to the above, South Park series is a good place to look!