After reading this this great how-to on instructables (via Lifehacker), I put one together using a carriage bolt, D ring and a shoulder strap from an old messenger bag.
Bonus: Because the strap has two clips, it can be used to stabilize the camera by unclipping one side of the strap, standing on the loose end of the strap and lifting the camera up. As long as the strap has tension, it will hold the camera steadier.
Small piece of 1/4 inch thick wood.
Shoulder strap from a laptop case/ messenger bag.
First, I drilled a hole in a 1/4 20 carriage bolt. (1/4 inch, 20 threads per inch). It's pretty common. I usually have quite a supply in my scrap box. I've used them on my telescope, flower presses and various other projects. The hole was big enough for the "D" ring that I planned on attaching.
After the hole was drilled, I cut out a 1 1/2 inch diameter circle of wood from 1/4 inch maple. The wood acts as a washer to keep the "D" ring from pressing into the camera.
Note that I have two different hole saws in this photo. The one on the left can be used in a hand drill, but the holes are a bit rough. The other is adjustable, cuts very clean holes, but can only be used in a drill press.
The "D" ring was attached to the carriage bolt. Twist the D ring to open it, don't stretch it. After it's on the bolt, you can twist it back together. That's how the piercer did my earrings when I got my piercings. If you stretch it, it will never go back together right.
A few drops of glue were applied to the top 1/4 inch of the carriage bolt, where the wood disk is going to go. It might take more than a few drops, make sure there is enough. The wood disk was placed on the bolt, then a washer and a nut. I tightened up the nut, to hold the wood in place while the glue dried.
I prefer Tightbond III wood glue. It dries water resistant and will stick to metal.
Clean up any glue drips with a damp cloth.
Cut off the bolt at the nut, then file it flat and fix up he threads so that it fits into the camera. The threads on the bolt are much nicer to work with if you cut the bolt, then remove the nut, then file.
Complete and ready to be attached.