3D Extruder, from Ben Rollason at AE Scripts, is a script that makes it easy to create 3D extrusions in After Effects, automatically "using the time-honored method of stacking 2.5D layers. The benefit of this is your 3D extrusions are part of your real After Effects 3D space so they interact properly with other 3D layers."
The script comes with ample training on light, reflections, bevels, and more. Be sure to see Ben's other 3D scripts and tutorials.
For other tutorial and methods of making 3D of text and shapes, see 3D Text in After Effects, a roundup at AEtuts+.
Here's Ben on his new script: