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 niche as this will help in quality organic linking - sites will naturally link to your site once they see unique and helpful information in your site. Keep in mind that the more targeted backlinks you build for your site, the more likely it will bring in the right visitors that could make the conversions 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 Postings - to high PR and frequently crawled sites
Social Bookmarking
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 how effective has it been?

I use these methods

Directory Submissions - targeted links at high PR directories
Blog and Forum Postings - to high PR and frequently crawled sites
Social Bookmarking

Im with Jlo. SES, social bookmarks, and buying links via adtoll and adbrite.

i have never spend single cent on adv

The last thing you really want is spending... but it is an option when you seem to have been doing everything you can to the best of your abilites and knowhow and yet still not being able to see results

when one can see nice results why spend money

Exactly my point!

Building quality and relevant link is an important factor in online marketing.

Quality link with theme related is benefited to get higher ranking in major search engines. However, High PR link is able to provide your site page rank high also.