The key to link-building is offering the other website something in return. There's no reason why that has to be anything like a link.
This is amazing. 99 Ways to Build Links by Giving Stuff Away (and Improve Your Brand Too) on SEOmoz is a huge list of ways in which you can give away products, time or money and get yourself some links in return. Links are hugely important. Far too many industrial and scientific companies still think that generating links to their website isn't worth spending time or money on, yet many of these then spend loads of money with SEO consultants who claim to be able to improve the company's position in the Google results. You can do so much of their work yourself, so much more cheaply, and key to this is link-building. And the key to link-building is offering the other website something in return. There's no reason why that has to be anything like a link.