I should be promoting my book, but for a while now I've been exploring options for selling 3D designs. The way I figure it 3D printers are only going to get cheaper, and people who aren't designers or creators are going to want something to print. To that end whoever has an established library of 3D printable objects already for sale will be ahead of the game. So I've been looking for a place to host a library of 3D printable models. There are already many sites out there where you can buy 3D models, but how are they for selling them? I set out to find out with a collection of small bird egg holders I designed.
Ponoko has proven so far to be the best. It has a clean interface, I can upload my models, edit them myself after upload, and manage my own storefront. 3DBurrito and 3DLT both required an administrator to do anything, it was a pain in the neck. Ponoko doesn't take commission from the models they sell, they make their money when they make it for you, so 100% of the sales price for the model goes to me. Plus Ponoko will sell you the STL, not some DRM laden file format, that you can have them print it, print it yourself, or have someone on MakeXYZ print it for you. The only problem I see is Ponoko is not a very easy name to remember. I think I'm sticking with Ponoko because it just works... until a more compelling reason comes along to try something else. (So if you've got another service I haven't tried, let me know in the comments.)
PROTIP: If you want to sell 3D models be ready before you start making the listing. Have the models made, tested, if you can, and an image ready, either a picture or a render that will really sell the item. Thingiverse may be cool with you being loosey-goosey with the edits, but when selling you need to step up your game.