I just finished quick project I thought you might find interesting: A homemade "porteur rack" for my Bridgestone MB2 errand bike using about $35 worth of supplies available at any hardware store and an extra Park Tool Handlebar Holder I had lying around (you know, the $17 thing you slip over your top tube and the handlebars to keep them from turning while your bike is on the repair stand). Parts included some 1/2" x 1/8" steel strips for the supports, two 14" x 6" x 1/8"oak strips for the top, 1" x 1/8" aluminum strips to support the wood, and a few p-clamps and nuts and bolts to hold it together. Oh, and a can of black Rustoleum spray paint.Ron, by the way, also owns the Meral randonneuse we feature on our Flickr site, and he sold us the Eisentraut Limited for which I'm slowly gathering parts, so he knows fine bikes as well as homebrew beaters.
I used a re-bent curtain rod bracket to attach the rack to the fork crown hole for added stability. The hooks on the front of the Park Handlebar Holder provide an easy way to attach a bungee cord or net to your cargo and the loop at the other end keeps your cargo from sliding into your brakes. The finished rack is surprisingly strong, rigid and rattle-free. It was just luck that the Park thing is the same color as my bike. I wish I knew how to weld!
So far I've only put about 15 pounds on the rack, but I'm sure it can handle more. And the funny thing is the rack actually improved the front-end stability of the bike; I can now ride hands-free at slow speed without any wheel flop. Maybe that's to be expected, but I was worried that the contrary would be the case.