Arch Linux
Arch Linux is a minimal Linux distribution, meaning that you install what you want and not what others want to install for you. Arch Linux is available for i686 and x86_64 processors, though currently there is a port for PPC being worked on.
Arch Linux uses pacman for it package manager so you can install applications easily. For example, if you wanted to install pidgin, you would run pacman -Sy pidgin and it will download and install pidgin. It is also easy to upgrade your system, by running pacman -Syu. Arch Linux is a rolling release, so you don't have to reinstall your system in order to get a newer version. Which, arguably, is better than having to possibly redo your current setup.
If you would like more information, you can vist Arch Linux's site at ArchLinux.org