DoFollow Blogs Search Engine
For the comment spam prevention, in the early 2005 Google engineers recommended adding nofollow tag on links that can be generated by users (blog comments and so on). This became a de facto standard, and major blog publishing systems such as Wordpress applied nofollow for comments by default. Later, a DoFollow movement began. DoFollow is a wordpress plugin, that disables the nofollow links. And DoFollow is considered now a great way to encourage comments and attract visitors.
So, many blogs provide comment links without "nofollow" attribute. And commenting on such a blogs is a good method to get a quality backlinks on your subject.
This search engine will find the blogs without nofollow tag in the comment links (with DoFollow plugin installed). Unlike other services maintaining huge lists of do-follow blogs (which are not always up-to-date and tend to contain some expired data) this service is based on the live queries against the current Google index. Just enter your preffered keywords and get the results.