We have founded a 3D printing marketplace called FabGate:
Currently we have 11 manufacturers on FabGate, who offer 14 materials for printing 3D models. FabGate is completely transparent: it is also possible to communicate with the manufacturers (after sending a request). You can also share your models with your peers on FabGate.
Check it out! Let me know what you think about it and what we can do better.