With 6" of bell wire (~18 gauge) and the lid to a ball point pen, I improved the range of my Gadget Infinity wireless trigger from less than 20 feet to more than 200. (Final result here)
I just soldered the coiled wire onto the antenna terminal, and trimmed a pen lid with a Dremmel tool to fit in a 8/32" hole I drilled in the top of the transmitter cover. I couldn't believe it worked. My out-of-pocket cost? $0.
Caution: You can ruin your transmitter doing this. Consider yourself warned.
Lest I leave everyone with the impression that this made performance perfect, it does seem to cause more undesired flash pops. I don't know if that's strictly a result of this mod making phantom signals go farther, or the channel I'm using. I'll have to try different channels and see if I get fewer unwanted pops. That being said, the number of misfires was really low. I probably got 95% hits on the first attempt at a shoot.
Update: It's very channel sensitive. One channel pops randomly like a dance party. Another channel is perfectly well-behaved.