a good place to start for appearance is http://www.gnome-look.org
as far as apps go, here's what I have running: VLC (multi-format media player), songbird, deluge (GNOME BitTorrent client), Eclipse, GnomeBaker, Avant Window Navigator (OS X-like dock), Blender (3D authoring software), Inkscape(vector imaging), Picasa, some others... of course, all the plugins, apache, languages / libraries for whatever you plan on running...
There are a lot of different ways you can go with it; it would help if you gave an idea of what functionality you 're looking for. Is this for strictly dev, or do you do image / graphics work, etc? The Ubuntu forums are a good place to start.