I've been interested in the theoretical parts of game design for a long while and found the wiki page tvtropes.org just recently. It contains classifications of common elements in all kinds of media and fiction, interactive and not. It turns out none of my own ideas are in the least original, but at least now I can stand on the shoulders of giants :)
http://tvtropes.org/pmwiki/pmwiki.php/M ... gameTropes