FanFiction.net - The biggest online fanfiction resource, and a great place to find PPG stories too!
Chaotic Skies - A relatively new BB for the darker side of Powerpuff Girls fanfiction. Run by SliferSkyDrgn and Neo Larry.
Parsec's PPG fiction site - a part of his old site. A new site is on the way, I think... :)
Casualty FanFiction - My sister's website, devoted entirely to the hit BBC shows "Casualty" and "Holby City", as well as some "Star Trek: Enterprise". Ceased updating.