Here’s a quick tip: How to get lines (without freestyle) with solidify modifier and back-face culling. 2 setups, a. for GLSL viewport, b. for Blender Internal renderer.
Note 1: This only produce “Silhouette” and “border” edge type (Freestyle equivalent).
Note 2: Please make material #2 untraceable by unchecking “Traceable”
Update: Outline material node setup for Cycles by Colby Klein
Update #2: Variable thickness with vertex group and weight paint