I agree that the stock horn is pretty lame. I picked up a set of Fiamms at Crappy Tire:
http://www.canadiantire.ca/browse/product_detail.jsp?FOLDER%3C%3Efolder_id=140847439 6672431&bmUID=1210336453893&PRODUCT%3C%3Eprd_id=84 5524442457759&assortment=primary&fromSearch=true
They work well, are sufficiently loud, and have a very nice European tone
. And the price is right.
I mounted them in the stock horn location, and used a relay that I tapped into the stock wiring. Try to mount them as high as possible, to keep water out of them. I had a problem with that.
JD