Well I used to have, and user BUT!, all the blogs from the list used to have like 1000+ links from the comments, so complete trash.Be aware if you are planning to pay cash for such a list Send me a PM and I can give you examples, but for free offcours. Can be usefull only if you are in a middle of a crysys or something and you have to show to somebody that you can build links, but I dont recommend that. But sometimes this approach can save some deals.
I can give you a tip how to find do follow blog list...just go to google.com, and search automatic do follow blogs and the PR you like to put..
no quality blog can have instant approval on comments. any blog having instant approval is spammer's paradise and you dont want your site listed there
Blog comments are useless, specially on popular content management systems. If you can find blogs using user made CMS like mine you may have a chance.
Do follow blogs help to improve your ranking position and drive huge traffic to your website. It is better to comment on do follow blogs. http://niceblogger.com/2009/08/21/dofollow-list/
Right now auto approving dofollow blogs are spammed like hell. I don't see any benefit form them. Instead you can try out dofollow social bookmarking sites. You can find a list here http://www.crazyblogger.info/blogs-stuffs/how-to-develop-backlink-and-rank-good-in-search-engine/