ModDB

From the latest of the ModDB front page, development toolkits for a large group of games have been released! This includes:

Mirrors Edge Level Editor:
http://www.moddb.com/games/mirrors-edge/news/mirrors-edge-level-editor

Braid In-Game Editor:
http://www.moddb.com/games/braid/news/braid-editor

Dragon Age-Orgins Toolset Beta:
http://www.moddb.com/games/dragon-age-origins/news/dragon-age-early-access-beta

City of Heroes Architect:
http://www.moddb.com/games/city-of-heroes/news/city-of-heroes-user-made-content