Link building is the key for an effective SEO campaign.  This works best for
 PR and SERP.  Always provide useful and relevant content in your websites n
iche as this will help in quality organic linking - sites will naturally lin
k to your site once they see unique and helpful information in your site.  K
eep in mind that the more targeted backlinks you build for your site, the mo
re likely it will bring in the right visitors that could make the conversion
s for better revenue.  You do targeted link buidling for fast and long term 
traffic to your sites.

There are several ways to build links.  Here are just some of the following:

Directory Submissions - targeted links at high PR directories
Blog and Forum participation - to high PR and frequently crawled sites 
Social Bookmarking 
Press Releases
Classified Ads
Article Marketing - submit to high PR directories, could also serve as link 
baits
Link Exchange - with relevant and authority sites
Link Baits - for organic linking
Etc. etc.

What are your thoughts?  What kind of link building method do you use and ho
w effective has it been?