I spent a while searching the net for new themes.
This site seemed to have the best ones available.
http://dailymobile.se/category/nokia-s60-themes/
I've tried a few and obviously its all down to personal preference but they all work and most of them are much better then the standard ones.
Just download from their forum to your desktop, unzip and then transfer the file to the install folder on your phone. Unplug your phone from the USB and go into the app manager, under installation files click on the themes you have just copied across to install them.
Then when you go to change theme it should be available to you.
PS. I found out that for some themes if you install them on to either mass storage or the memory card that when you connect the phone via usb the theme on the phone disappears and reverts to the default theme. To avoid this install the theme onto the phone memory and this will cure the problem. Obviously we don't have much memory there so if I were you I would only install your fav themes after checking them out. But file size of these themes are usually small, like less then 1mg. Also it seems random to me which themes this rule applies to, so some maybe fine in mass memory and some may not. All trial and error.
Have fun.



