Let's also include a list of types of sites that will encourage user generated content:

Forums
Blog comments
Give away blogs and webpages
wikis
classified ads
auction
Social Bookmarking
MySpace
Article directory
YouTube
Flickr (pictures)

All of the above could be adapted to big and small niches and will give you free, unique, quality user generated content.

You'll also get repeat visitors, bookmarks, etc, which will also help with any People Rank.

The down side is, you need to have lots of traffic BEFORE you can make these types of sites work.

If you know of any free/good scripts that will build these types of sites, please add them to this thread.