Principle - Sponsor an event, online or in-person, and receive a link from the event's website, and possibly those bloggers/site owners in attendance. Locate events with geographic proximity or topical relevance (search engines are useful, but events calendars like those on Upcoming.org & Craigslist.org are valuable, too). Get in touch directly and offer sponsorship. Depending on your level of aggressiveness, you can directly ask for a link or simply cross your fingers that some will appear.

In my experience, if the audience/attendees are relatively web savvy, links are very likely. Even if you don't get a link, or it's devalued, the side benefits of networking, goodwill and branding are valuable on their own.

Example - SEOmoz sponsored a local Startup Weekend event here in Seattle this year, and received a link from the "thanks to our sponsors" post, as well as several related blog posts.