Click on the diagram for details and photos.
Here's a diagram of what it looks like:
As you can see, I have a variation on the traditional folded dog leg. It's certainly not that elaborate but it keeps the modules from gathering dust and it allows me to run as many as two trains at once.
I can run a single train on a twice around arrangement that uses the helix, or I can throw a few switches and run two trains on two independent loops.
Typically I run a through freight on the outer loop and a local freight on the inner loop. Cars are shuttled between them via the interchange track at the yard.