My most recent use for them was to create a "shield" like the Wingshield. I don't really want the screw terminals, so instead I wanted something that I could still use regular jumper wires for quick prototyping. I figured I could cut up some perf board and make something that would allow me to split the input and output headers.
Step 1: Parts
I trimmed 4 pieces of perf board that gave me a nice little handle on one side, but nothing on the opposite side so each header wouldn't interfere with the next one. I had to make them 4 separate pieces because the space between each bank of headers is less than the width of one pin on a standard perf board. I thought of taking a standard Arduino Protoshield and cutting the outer edges off with a Dremel, and while it would have been easier, it would have been a waste of a good Protoshield. This way, I was able to spread the additional female headers out 2 pins, where the protoshield would have had the new headers right next to the old ones.