If you search for "themes" with your package manager of choice (Synaptic is a good one) then there are quite a few that you can install. And, yes, Gnome-look and Xfce-look are good places to go. One thing I've noticed with themes, though, is that they mostly fall into three categories: bland grey, shiny black, and garish.

Every now and then I try my hand at themes, but I never seem to get around to packaging them up for other people (with two exceptions; my Celtic theme which I submitted to Fvwm, and my CedarBrass GTK theme which I put up on one of those *-look sites but I can't remember which one now).