Ask HN: Best practices for keeping cloud server secure? (linux)

I'm able to take a basic linux distro (stable Ubuntu Server) and install everything I need to get my web apps up and running. (Django, Rails, PHP etc...) But after all of that I would appreciate some advice on security.

Here is my current checklist: 1. Change the root password assigned to me 2. Add admin user so I don't have to log in as root 3. Change ssh port to something random I make up and require SSH Key 4. Set up iptables to block nearly everything except (80, my ssh port, and maybe a couple of others depending on requirements)

What now? How do I keep the server up to date? I really don't want to have to read the ubuntu-security-announce mailing list daily I just want to build web apps.