MeshLab is a great free editing tool for 3D models (originally designed to clean up 3D scans) and features many options, including some fun rendering options and converters. I have used it a few times as a quick alternative to bigger apps, like Blender.
Since a couple of months, I’m a super happy user of MagickaVoxel. It’s a free voxel creation program with a very intuitive interface (okay, mac users have to relearn a few things) and great export functionality.
Get it here: http://voxel.codeplex.com/
Models can be exported for all sorts of purposes and for 2D exports, you can choose various shaders…
… and camera modes, including isometric and other orthographic views…
…they even have plenty of rendering options, such as lighting, grain and even focus shift…
Even a 3D slacker like me can get great stuff done and if you are a pixel artists, get ready to add a new dimension to your work.
Crocotile3D is a super simple tool to turn 2D Tilesets into 3D scenes. The app is limited to dragging 2D planes into a 3D space and arranging them into 3D objects and scenes. But that limit makes it work really well and really really fun to use.
A lospec charac like this legionnaire just took me minutes to complete. So if that kind of stuff is your thing, give the program a spin and consider purchasing a key to access saving and export features.
Check it out here: http://www.crocotile3d.com/
TEN24 is all about 3D scanning of people and providing 3D models and 3D viewers for reference and stock purposes. Their scans are quite fun, especially when they scan their models in motion, seeing all the muscle deformation in a 3D model is pretty wild.
They have been cool enough to dump a big bunch of free turnarounds based on scans onto their site for artists to use as reference. This is great for model sheets and turnaround design sketches.
You can get the stuff here: http://www.anatomy360.info/anatomy-scan-reference-dump/
They also sell model packs in their shop: http://www.3dscanstore.com/