Probably the best one at the moment is Framework Design Guidelines: Conventions,
Idioms, and Patterns for Reusable .NET Libraries (Microsoft Net Development
Series) (Hardcover)
by Krzysztof Cwalina, Brad Abrams (
http://www.amazon.com/gp/product/0321246756/sr=8-1/qid=1154355021/ref=pd_bbs_1/1
02-2225499-8768147?ie=UTF8).
These guys were on the CLR team and know what they are talking about. The
book discusses a number of specific cases that arose when writing the .Net
framework and the thought process that was used to resolve conflicts as they
arose.

Jim Wooley
http://devauthority.com/blogs/jwooley/default.aspx