Technet have a post which lists all the Microsoft Blogs, currently there are 262 blogs listed in 38 sections.
Below is the sections and here is the link to the listings, this includes the link to the corresponding Rss feeds.
1. Business Process Management
2. Consumer and Hardware Solutions
3. Dynamics
4. General
5. Industry Solutions
6. Internet
7. Microsoft Advertising
8. Microsoft Conferences and Briefings
9. Microsoft IT and GFS
10. Microsoft Learning
11. Microsoft Licensing
12. Microsoft Online Services
13. Microsoft Press Pass
14. Microsoft Service Management
15. Office Applications
16. Office Online
17. Office Sharepoint MOSS and Groove
18. Partner and Customer Resources
19. Planning Deployment and Update
20. Product Support
21. Research and Labs
22. Search
23. Security
24. Security Products Forefront
25. Software Development Shared Source Initiative
26. Software and Web Development
27. Software and Web Development Cloud Computing
28. SQL and Business Intelligence
30. Systems Center Systems Management
31. Unified Communications
32. Virtualization
33. Windows Desktop and Embedded
34. Windows Live
35. Windows Mobile
36. Windows Server and Infrastructure
37. Windows Server Networking and Remote Access
38. Windows Systems Management