First let's make a master list, all the usual ways we can think of to get quality, relevant links back to a website.
1. Fill out a form or email a webmaster, asking for a reciprocal link.
We'll assume for the purpose of clarity that we mean exchanging links to post to a traditional directory page.
2. Deep linking.
You embed your partner's link into relevant text on a page other than your directory page, and your partner does the same with your link.
http://all-seo-tip.blogspot.com/search/label/Backlinks