We have the free software program Top 10 Blog Comment which is Free: Here is how it works Enter in keywords Press the search button. The software will do a Google search for the first 10 results (first page) for each keyword. The software stores all the web page urls. Press the Find Comments button. The software scans the entire list of urls from step #2 and lists all of the blogs that allow comments. The software DOES NOT auto comment for you and this is NOT something you want to do. Google will tag the url you post in the comments as spam (because of the volume of comments) AND most blog owners will know it is spam and won't approve it. The software is not on cnet and softpedia and got a 4.5 out of 5 stars.
Check out Top 10 Blog Comment on Cnet http://download.cnet.com/windows/affiliate-switchblade-software/3260-20_4-10451397-1.html or Softpedia http://www.softpedia.com/get/Internet/Search-engine-tools-submiting/Top-10-Blog-Comment.shtml
Scrapebox for quick and dirty blog posts, but not the best IMO. My favorite tool is WP Robot. It's so easy to use and there are so many sources it can pull data from.