There are a few ways to do this; the techniques already mentioned are excellent, and should be fine for 99% of your needs.  The result produced by **Warlock279** is one of the best I've seen!

Still, I decided to take a different approach with my attempt.  I started by using simple edge-extrusion techniques on a single-sided plane, with some additional cuts and symmetry.

The result is all quads, and manifold (very slight thickness); which could be useful for rendering in some physical render engines, or using softbody dynamics for animation.  The topology is still very light, but it could also accept subdivision, if need be, for sculpting additional surface details, like wrinkles or noise, for baking out to normal or displacement maps.  The downside to this technique is that it is not intended for animating the folding process, as it does not follow realistic folding patterns to create the shape.

The non-manifold version is 50 quad polygons; the manifold version (thickened) is 128.

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