If you do a search in quotations for "powered by soapblox" those sites are all do-follow for comments that you leave.
there are a million of these threads + check google for do follow list and you will see a TON of already put together lists to take from. A better method however, build your own list of sites so you can have your very own master list to work with. I have been working on mine for awhile and am proud of it compared to simply grabbing harvested lists. Always a plus to check them yourself and make sure they are UP. Don Luttrull
You could also use tool like dofollow diver or comment kahuna to find dofollow link sites where you can put blog comments upon.
I just add in the no follow firefox plugin and when I come across a blog that I like I can quickly see if it is a no follow blog.
Here's a list: http://www.idofollow.info/search/label/65%20More%20Dofollow%20Social%20bookmarks Code (markup): Its a list of dofollow social bookmarking.