-Contact related sites, offer them content.

-Use Guest blogging services like MyBlogGuest, BloggerLinkUp. There's also Haro if you're an expert in your niche.

-Look for bloggers with just one adsense unit and a donate button. You know the type. These usually are passionate about their content and would probably accept a small donation to link to your related site.

-Look for resource lists related to your niche. If they're old and curated, they'll probably have broken links on them. Email the owner, point out the broken links and suggest new ones. Yours included.

-Looks at your competitors' backlink profiles. Buy/Acquire/Build/Trade to get the same links they have. But do it like you're making a mix CD, only the best tracks.

-Acquire related domains with PR. Make sites out of them separate from your own. Since you like creating good content, it shouldn't be hard. With these sites, you can be less whitehat about the link building. I blast them to hell.

It takes long and that's why you should be doing it for a niche worth the while. Don't have the time or the patience? hire someone cheap to work for you.