I love Avatar to teh point of nerdiness. I am cosplaying as a na'vi for a convention soon and have been working out like crazy to get into the right kind of physisce. i also have bought the "pandoran wildlife guide" and am learing teh na'vi language. I also opreordered the DVD release the instant that it became available, and picked it up from the video store as soon as it opened. I know my name, and the names of all my friends in Na'vi, and also know a few phrases. I know both the human names, and the na'vi names for all of teh creatures that were seen in Avatar as well, from the Thantor to the Leonuptrix. Basically... if it has todo with Pandora, i know it and love it (knowing the stuff actaully makes the movie a LOT better)
I have a similar passion with gundam, having memorized lines, bios and mech stats for a large number of suits. I also collect gundam models and put them togehter.
Star wars and star trek are lesser nerdy passions, but still fall into teh range of fans.
Basically, i find the realy world to be vastly overrated and like sinking into teh very depth and core of fictional worlds. That, and i like being nerdy, it is part of who i am! Hooray for nerds, long live the collective!