Note: This post is for my own reference.
3D Printers
Google Doc
prusa3d.com
printm3d.com
3D Files and File Sources
Thingiverse.com
M3D Models
3dshook.com
myminifactory.com
yeggi.com
cgtrader.com
pinshape.com
youmagine.com
grabcad.com/library
123dapp.com/Gallery/content/all
3dvia.com
instructables.com
cults3d.com/en
repables.com
libre3d.com
Other
shapeways.com