I'm holding out for the loudest, baddest, scariest, wailingest, meanest horn money can buy. And before riding season commences again... that will be the horn I have on my bike.
I got one! Used it a couple of times already, does the job!
Before, the little "meep" from the stock horn would never wake any of the drivers here. Got this bad baby and now, I just feather the horn button to make people go back on their original track, should they show the intention of pushing me out of the way.
http://www.aerostich.com/ear-cannon-air-horn.html
PS (I got the Korean copy of it, but it works the same...)