Since I do it a lot I have a list of 74 that I use ( that allow signature and mostly are do follow ).
Also I have a list of about 150 that I tried but from various motives I don't do there forum posting.
Forum posting, if used right, is a mine of gold as a backlinking method and rising in the serps. But you have to choose some authority forums with high pageranks and related to your niche and try to make relevant posts not to be considered a spammer. Respect the community and the community will help you grow.
Most forums, like Daniweb, use 'nofollow' so if you are looking for backlinks from this site, it's not going to happen. If you would like to contribute to the discussions and be a part of a community (like it used to be on here), please do. Spam posts are killing most of the forums which is sad.
One should always participate in forums of his experties, or if he want to learn something form a forum. Forums are a great place to learn and share knowledge and not just for the sake of some back links. Links to your site could be used if you want few more referals but must keep in mind if it is relevant only then you can get some targeted visits.
I participate in SEOChat, Daniweb and Webmasterworld.
All that forums that have a strong PR and is relevant to the niche of your website that impact a huge impact on your rankings as well as the traffic
Daniweb is a good forum but you can also search high forums in Google