If you are looking for Blogs to the various types of internet marketing there are several ways to find them.
Blog search engines like Technorati are a good source to discover blogs. Also blog directories can be a good source, but to be honest, there are so much blog directories out there that you will have a hard time finding one that has a good selection of internet marketing related blogs, let alone categoriezed by subject.
Here are some additional blog listings by topic:
Search Marketing
1. Search Marketing Blogs List by Lee Odden – Over 300 Blogs to Search Engine Marketing and Optimization.
3. Search Engine Marketing/PPC Blogs
Affiliate Marketing
4. Affiliate Marketing Blogs List by SuperAff.com
5. Bumpzee Affiliate Marketing Social Network and Blogs – List of included Blogs
6. Affiliate Marketing, Contextual Advertising and Affiliate Networks Blogs at Cumbrowski.com
7. AffiliateMarketing Buzz – Aggregated Feeds. See List of included Blogs to the right
Internet Marketing (Email Marketing, Web Analytics, Marketing in General etc.)
8. Internet Marketing Blogs at Cumbrowski.com
Plenty of Blogs to explore. If you are more into Podcasts and Video, check the Resources here.