Well, you got one good one - article directories. Link exchange is a waste of time. Google has devalued this. Oops - link wheels are great, too. Sure thing that you need to research this on your own. Don't rely on what's posted here (mine included, though I'm right) LOL!
There are lots of factors hurting the typical forum signature link. The quantity of the links in a typical thread, the weak weight trust and authority of a typical forum thread, the fact that they are artificial links (not merit-based or otherwise earned) are but a few of them. A good analogy I guess would be dollars and cents. The merit-based links I advocate and recommend people get are the dollars (oh, I forgot to mention "large quantities of large denominations"). Forum links are the cents. And I don't mean quarters or half-dollars either. I mean pennies.
Just the basic, Blog Post and Commenting---say something for teh content's sake; Forums Posting---contributing useful info; Article Submission---no duplicating and relible article website; Directory Submission---free one usually don't give u much help ,go for the paid one. Social Bookmarking--make u stuff unique enough for others to bookmark u. They are from my own experiences!
* article submission * forum posting * directory submission * blog * press release *social networking * link exchange * Social bookmarking * RSS Feed They are the couple that I find effective to build backlinks, basic but effective!
Here is a very good link resource: Building Links Resource and NO, forum signatures is not the best way to build links but it is a good resource. I belive it should be part of your SEO link building strategy but dont just spend your time on that. Mix it up, thats key.
Link building strategy: Use link backlink creation methods like article marketing, social bookmarking, blog farms, link wheels, reciprocal exchanges, purchased backlinks.
Dan Schulz: Much debate has gone on about whether linkwheels actually work to boost serps. Curious to know what's your opinion on this? Thanks.
Look for websites that share a common theme with your website. Professionally ask the site administrator if you could exchange links with their site. It is important that you only seek out sites with information relevant to your field of interest, as the quality of each backlink will affect your search engine popularity. Also, ask that keyword rich anchor text be used for each link.
I have had good luck with backlinks in forums as well. Go sign up as a member of some forums in your niceh and post away!
blog commenting and forum are still good for link building... other methods that are proven successful are guest posting, social bookmarking and social networking...