I would suggest grsecurity, since I'm the author ;) http://grsecurity.net I think it can provide you with the security you need, and it's GPL. Also many people seem to like my snort parser, which is available in the misc section.

I think this should be in the advertising forum:eek:

sorry, I meant to send it as a reply to someone's question about security software. hit the wrong button ;) grsecurity was recently featured on the front page of securityfocus.com 1.9.4 was released yesterday, and since then, 3000 people have downloaded it already. I've even made it easy enough for server owners to configure. You can install a pre-compiled kernel with grsecurity, or patch the kernel yourself and select from various security levels, or customize it yourself.