I noticed that forums are a great way to get dofollow backlinks. Simply place the link in your signature and post away.
However, there are tricks to doing this effectively. The idea to get lots of high pr backlinks is to find forums that allow dofollow signatures. Once you've found a forum that allows dofollow signatures the trick is to find old forum threads that have pr to them, maybe 0,1 or 2. Once you've found that thread you can respond to it. The main problem with this method is that your post will push the thread to the top. It will seem weird if you are constantly pushing 1-2 year old threads to the top. So you have to do it only like once per day and don't put your link in your signature just yet. After maybe 20-30 times of doing this let the last post sink to the next page. Now you can put your sig link in and it will appear on all the forum threads you listed. That will be 20-30 dofollow high pr links to your site.
Do this on a lot of different forums and you will get a lot of dofollow backlinks!