We have had the best success with quality content (and then submitting that content to social news sites like Digg, Reddit, Netscape, etc.) Another approach is to product "quality content" that is more than text, but is a tool people can use. Our Website Grader gets a lot of links for exactly this reason - it is a useful free tool that people like to link to.
Does this EVER work? I get these requests all the time, unless the site is completly unique, highly interesting, not in any way competing with mine etc, I wouldn't consider adding the link. As of this time I have never added a link like this although I have added sites that I thought qualified but did not ask. Anyone here added a link because of a request? (no reciprical or payment) by the way KH7, I'm not picking on you. I've heard a lot of people mention this method.
yes, content links and that too free, which people will link with there own self interest is always nice! i would say blog post and article links helps a lot, if you can't get it by your content, get it bought, as it is the same thing!
Create fresh and good content for your site. Based on my experience, forum signature, article, classified ads such as craigslist, blogs, tag, social bookmarking, and link exchange partners are the best way to get links.
To be successful in SEO today you really need a combination of all of these and other methods, there are no shortcuts.
In this case the key to success is the quality content that can attract the visitor let him no choice but to read it but the content should be unique and fresh.