From 3D printer manufacturer:
123D Gallery (from Autodesk)
Thingiverse (from Makerbot)
Treasure Island (from Pirate3D)
YouMagine (from Ultimaker)
Independent:
3D Via
3DAGOGO
Bld3r
CGtrader
Cuboyo
Cults
FabMe
GrabCAD
Pinshape - Find, share and sell 3D print files.
Redpah
Repables
Sculpteo
TF3DM
Uformit