Pacman 2.1 has new functionality to allow the use of multiple package repositories and multiple servers. This was brought about so we could open a new 'unofficial' package repository that will hold all the unsupported packages that never made it into the official Arch package area.
To start using the unofficial repository, just upgrade to pacman 2.1 and edit your /etc/pacman.conf. Find the block that starts with '[unofficial]' and uncomment it and the servers listed underneath. Then just run pacman as usual and it will check both repositories for packages.
This also opens up a new opportunity for the more adventurous: You can now create and use your own local package repositories. I often keep my own PKGBUILD files in /usr/abs/local and install them on to my box. Now I can turn that into a functional repository that can be used with the 'pacman --sync' operation. The new 'gensync' script will do the dirty work for you. See the pacman manpage for a crude explanation.