Some blogs I regularly read:

Written by Raymond Chen, a developer on the MS Windows team.  Great stuff if you want to better understand how Windows works, particularly the shell.

Written by Mark Russinovich of Sysinternals fame.  Great info on Mark's tools and books as well as his work with Sysinternals.

Written by Euan Garden, Product Manager in the MS SQL Server product group.  Euan's always got good stuff about the user community and cool features in the product.

Written by Slava Oks, a developer on the SQL Server team.  Great info on SQL Server internals and the server's interaction with the OS.

Written by Kent Tegels, SQL Server MVP.  I read this one because Kent posts often :-).  Seriously, it's good to see an outside perspective on the SQL Server user community.