Check out this site: http://distrowatch.com/
and if all else fails, google. (actually you're better off starting with google
Other good beginner distros (short for 'distribution': different 'flavors' of linux): linuxmint, mepis, openSUSE, ad infinitum (almost). There are literally thousands of different linux distros out there; everyone has their favorites. Backtrack is a distro designed specifically for forensics and penetration testing of systems and networks (and therefore tends to lend itself more to advanced users). Try one of the more beginner-friendly versions first; pick one and have fun!
And (belatedly) welcome to LQ!