Using libigl and Mesa3D's off screen rendering is was easy to whip up a QuickLook preview and thumbnail generator for our favorite 3D model file formats. I opted to avoid Xcode and compile the application using a good old Makefile. You can find the project in the libigl examples libigl/examples/quicklook-mesh/ (as of version 0.3.2).
Once installed the QuickLook generator will make (static) previews of any .mesh, .off, .obj or .wrl files when hit [space] after selecting the file in Finder.app.
Or when you use one of the fancier Finder.app views
I imagine I'll be perfecting this over time, but for now it shows 6 canonical views and uses a double-sided material to give you an idea of any inconsistent mesh orientation issues. It should work for triangle meshes or general polygonal meshes.
You can skip compiling and just download Mesh.qlgenerator. Install it by moving Mesh.qlgenerator/ into /Library/QuickLook/. Then either restart you computer or issue in a Terminal:
qlmanage -r
qlmanage -r cache
Update: I've finally fixed some issues with the dynamic libraries. The updated Mesh.qlgenerator now contains a binary which should work anywhere, without requiring you to install Mesa3D or any other dependencies.
Update: I've moved this out of the libigl/examples to its own repo on github.