Smallville
I am starting this particular section off with the one story that totally sucked me into the fandom. For Smallville, it was Lanning Cooks Identical Series. Has there ever been a better story? Find it here: http://lanning.slashdom.net
And for some extra fun, go here: http://www.livejournal.com/users/elandrialore/34962.html for a songvid teaser for the story. Yes, Lanning has many avid fans and for good reason.