I'm creating a list of easy to comment on DoFollow blogs. All of them will have high PageRank so you'll know your links will be safe.
Blogspot Blogs!!! Did you know that in Blogspot blogs you can leave the URL of an individual blog post instead of the whole blog? It makes for good SEO because there is also internal PageRank to worry about.
*So instead of 'http://myblogs.com' you might want to leave: 'http://myblogs/mylastpost/may18/
Too many comments on a fav blog??? I've noticed that some bloggers mess up their PageRank by leaving too many comments on one site. You can get away with having a favourite blog and leaving several comments. After twenty or so you should link back to a profile page.
'failblog.org' has a PageRank of 7 and is also DoFollow. However, people in the comments section get into the habit of conversing with each other. There you'll find a couple blogs that are a few years old and aren't properly indexed by Google. If you leave thousands of comments heading back to your site Google will see this as a form of link spamming. You'll be PR=0.
It's also important that you don't just leave a lot of comments on high ranking DoFollow blogs. Make your link building look natural. Go to Google Blog Search and find blogs that have similiar topics to your own: Leave comments on some NoFollow sites here and there, too