Hah, that's funny: The word "ginormous" made it into this year's update of the Merriam-Webster dictionary, two years after it made first place in an online poll for the "favorite word not in the dictionary".
They define it as:
extremely large, HUMONGOUS
Awesome.
(via bb)
Update: As a reader points out, it only wasn't in Merriam-Webster (an American dictionary) yet -- while it has been British slang for a long time and thus can be found in the Oxford dictionaries. Thanks, Ian!