IMO, the best content is User Generated Content, where you get your readers to write the content for you...

Here are some suggestions for User Generated Content:
Forums
Blog posts
Niche Article diretories
Niche Video site
Niche Myspace
Niche Craigslist
Niche Auction
Niche Bookmarking Site

Just as some gurus say "money is in the list", I say for SEO you should try to focus your efforts on generating and collecting User Generated Content.

SEO is all about "words"...If you can get tons of people writing words for you, you're well ahead of the SEO game. There's many forums and other sites that don't do a bit of SEO, yet get tons of SE traffic, simply becuase they have so many words on so many pages that something is bound to rank well...

If you have other suggestsions for content, including any scripts that will work for my list above, please post them below...

Thanks.