You can also check Synaptic for the gnome-themes package. There are some additions in there. The gnome-themes-extras package does not work (as per the Mint 6 release notes), but the community-themes (Ubuntu community) look pretty good, though I usually prefer lighter colors. They are an easy install via Synaptic, and an easy uninstall if you do not like them. There are several icon sets sprinkled around in there, as well. Have fun.