Hi there,
Here is a good list of do-follow blogs with PR8 to PR5:
http://www.uoo1.com/vb/2009/10/the-ultimate-do-follow-blog-list-with-high-pagerank/
Please note that 90% of these sites moderate their comments, so spamming them wont work, your comments will never get approved this way. For sites like Cisco, you do have to be inventive to come up with a relevant comment. It took me more than an hour to comment on all of them.
Note: on the list there is a site that stands out. Its the blog of a french lawyer with PR6 and its a backlink party! Just check the comments on any of the blog posts. Such a joke!
http://frederic-rolin.blogspirit.com/
Happy backlinking
Mikael