I've been experimenting with various types of foundationless frames. I've used the Popsicle stick in the groove, Kelley F-type foundationless frames, and a couple of my own design. All work, but I've had the best luck with the bees building straight, even comb with the following design (sorry, this is a used frame that I took cut-comb honey from, I didn't take any pictures before I used 'em):
The top bar is cut @ a 45 degree angle, and one of the scraps from those cuts is used as a triangular bottom bar. My first frames didn't use the triangle bottom bar, but after trying it out, I find that the bees attach the comb to the bottom much more quickly and regularly than frames with a flat bottom bar.