I am trying to find only blogs talking about a certain topic (where you can comment). How can this be done? By using Google? What about forums? Is there an option to search only forums, let's say vBulletin or phpBB based forums?
There are two ways- 1. Try to look into blog directories to choose your required niche. 2. Try to register in entrecard.com and can get most of the blogs with dofollow tag. Here also the blogs are categorized according to the topics. Hope this helps you to choose your favorite topic blog
Use this query to search WP blogs: “your keyword search†powered by wordpress “leave a comment†replace the your keyword search. There you go.
Just Google it. Type your Main Keyword + forum and hit enter...you can get many forums related to your niche. Good luck.
I would suggest visit mybloglog, blogcatalog kind of blog networks and make search with the keywords of your niche to find the targeted bloggers
http://www.blogsearch.google.com works really well for this. Also what I presume you are looking for are do follow blogs, that will provide you site with some link juice. Here's a list compiled by another DP member http://myseoblog.net/2008/05/11/list-of-dofollow-forums-with-dofollow-signatures/