http://www.gamepitches.com/ (just discovered this, via TCE):
The repository for video game pitches and design documents
This site serves to be a free resource to game designers offering them the web’s largest single collection of game design documents and game pitches.
It says “resource got game designers”, but … pitch documents are hugely valuable to anyone working on the business/funding side too. (there are two aspects to the site – design docs, and pitch docs).
…and if you work for a studio or publisher, perhaps you could ask about getting some of your company’s old pitch/design docs put up online?