You might want to consider Crunchbang Linux (http://crunchbanglinux.org/). It is
an Ubuntu derivative that has low overhead and uses Openbox with GTK support. It
is getting good reviews. There are three versions: regular, lite (fewer apps)
and Cruncheee. It uses some well known programmes and replaces a few with lesser
known ones to improve performance. You can see a list on their site. Crunchbang
is another name for the #! prompt, also called a shebang used in scripting. Fun!