You should see the apartment now... there are literally hundreds of project boxes strewn all around me. I've been on a buying binge in search for the perfect set of project boxes, enclosures, and cases for Arduino circuits. In my search, I even got frustrated and built my own case out of carbon fiber. Of all the cases, these are the best I was able to find... in each case (no pun intended), my goal was to find something cheap I could carry with me, and that would protect a simple circuit or Arduino while it sat in my pocket.
A tiny, business-card shaped carrier that fits a Lithium backpack and a simple circuit perfectly:
Purple Zipper ClamShell
Sometimes I just want to carry the Arduino, with a battery, and a simple circuit. This one works perfectly, and you can even fly with it (I've tested it at several airports, and security never questions me like they do when you fly around with exposed components in baggies)!
You have no idea how hard it was to find something like this. It's basically like a fishing tackle box, but much smaller, and sized just right for resisters, IC's, timers, switches, and LEDs:
I still think this one is so cool, and one of the best cases out there, so here it is again - the Ballistics pack...
Please let me know if you've found any good cases for projects - I'm always on the lookout!