I'm using the industry standard aluminum pipe size and spacing, so it should be possible to combine these printed parts with commercially available parts and/or rigs, though I have only tried that once with a part for a friends rig.
All the parts are designed in OpenSCAD and those source files are included here, in case you want to modify the parts to work with other pipes, differently sized screw, etc.

In addition to the parts listed here, you will also need a bunch (16 pcs for the pictured rig) of these (http://www.thingiverse.com/thing:11848) little thumb screws by Habbycam. It's designed for 1/4 inch, but I'm using them with M6 without any major problems. 

You will also need some aluminum pipes. The main pipes have an outer diameter of 15mm and the two handle pieces have an outer diameter of 20mm. I have found that the fairly cheap ones in the local hardware store can vary in dimensions, but it's what I use in my rig. Sometimes you will need to trim the parts a little bit to fit the pipe, at other times you might need to adjust the drawings (via the OpenSCAD files) to fit your pipes.

The foam handles are for a kids bike and also from the local hardware store. The foam shoulder pad is just a left over piece of foam that has been covered in nylon cloth and mounted in the shoulder piece with velcro.

To put everything together you will also need some screws and nuts. I use M6 for everything except mounting of the Manfrotto sliding plate, that one is mounted with 4 pcs M4 screws and lock nuts.

I am using a MANFROTTO 357 SLIDING PLATE ADAPTOR to mount the camera, but if you don't want that or want to use a different quick release plate, I have added holes in the middle of the camera plate for a 1/4 inch screw (with thumbscrew) that mates with the camera tripod mount or quick release plate.

In addition to the rig itself, I have also added a few parts to hold an audio recorder like the Zoom H4n (h4n_holder.stl and h4n_mounting_clamp.stl) and a little clip to hold the camera strap in case you use one of those (strap_clip.stl).

The lasercut_parts.pdf file holds two designs for cutouts in 2mm corc. Those are intended to be glued onto the camera plate and the H4n holder, to help ensure a good grip without scratching the mounted equipment. When mounting the Manfrotto plate, you don't need this corc piece.