If you enjoyed Managing Your AWS Credentials (Parts 1 and 2), I recommend that you check out Shlomo Swidler's latest blog post. It builds on the foundational information in Parts 1 and 2 but then covers a lot of new ground and proposes some very workable approaches to managing credentials on EC2 instances. Very useful.
Yeah, I know I could have just tweeted this but sometimes it feels good to type more than 140 characters.