Too my knowledge, there's only been two canon Tholian ships on screen. In TOS in one episode and once again in Enterprise. Both of the ships are shown in the above referenced site.
SFB has made an entire fleet of ships for the Tholians based off of the one from TOS. Desty Nova's site has very good representations of them. SFB also has the Neo-Tholian designs, which are of their own creation. Desty has done a few of them, as well. You might want to check out his page for reference. Unfortunately, nightsoft is down and the DL links don't work. You can still see the pics on his site though. If you need/want the models, I can send them to you.
http://members.aol.com/destynova02/myhomepage/Desty_Nova9.htmlI'd love to see someone take the Enerprise series PC and make up a set of Tholians based from the SFB designs using that PC. It's a lot better looking, IMO, than the old TOS design <hint>