As stated by Tom, creating useful helpful and interesting content and adding it to your website Is the best long term strategy for link building. Over a long period of time useful articles are highly likely to receive some links. What's often not mention is the value you gain from blog traffic. Even if no one links to your blog you will gain more traffic to your website. I've had many resulting sales due to our blog traffic. Not to mention you will be able to post your blog on blog directories (so you will at least get these links)
You could also create valuable content by building tools/widgets for your industry. Infographics are great to add to your blog and are often popular to share.
Other techniques you could employ is bog commenting (although comments must be relevant and add value to the conversion).
Hold a contest, you will be able to submit to contest website which will link to your contest.
Donate to charity. (often tax refundable, so if you have the budget It can be a win win for the charity and you)
Here's some links to some ideas for link building.
http://www.seomoz.org/blog/8-ways-to-buy-links-without-buying-links
http://www.seomoz.org/blog/99-ways-to-build-links-by-giving-stuff-away-and-improve-your-brand-too-14029
http://pointblankseo.com/link-building-techniques
There are heap of other techniques but you should spend most of your time building or buying valuable content. Think of high quality content as assets. While other techniques are often just expenses.