Tell what distro you're using from the command line

I've always wanted to know a command that will tell you what linux distribution you're using.

The answer is:

cat /etc/*release

The results for my current system are:

DISTRIB_ID=Ubuntu

DISTRIB_RELEASE=8.04
DISTRIB_CODENAME=hardy
DISTRIB_DESCRIPTION="Ubuntu 8.04"

Though it will hardly work on all POSIX systems, say my Mac for instance.