Caltrops has a rundown on Touhou Project (aka Shrine Maiden Project), the series popular “bullet hell” shoot ’em ups by Team Shanghai Alice (aka the mysterious Zun)! (So popular, in fact, that people apparently drop big bucks on arcade cabinets to play them in!)
Michief Maker, the author of the article, gives a brief overview of each of the games, which is accompanied by a YouTube video of the game in action. At the end he provides some info on how to obtain full versions of these games online.
See also: Doujin Shmups, an Introduction