I was looking around on the net for some downloadable themes for WSS or MOSS and found these – http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=0a87658f-20b8-4dcc-ad7a-09ad22641f3a.
This is a pack of 10 themes provided by Microsoft as a download. The download contains each theme as a Visual Studio 2008 project. If you open each one with Visual Studio and deploy it, a .wsp will be created allowing easy deployment to any WSS/MOSS Server. Screenshots of the themes included can be found below: