I regularly read two security blogs.
One is Schneier on Security. Bruce Schneier is a security guy who wrote one of the main crypto texts, Applied Cryptography, and a lot of other good books. He has a monthly email newsletter but he has transitioned to blogging, which I like.
The other is Edgeos. The RSS feed at the above link gives one an easy way to scan for new vulnerabilities and see if any of them apply.
Any know of any other good ones? Please comment.