I just replaced my stock horns w/ a set of Fiamm air horns. I LOVE them. They're blaringly loud when you need them, and you can give them just a light toot when you need to wake somebody up when a light turns green and they're sleeping.

The only issue is that the beep to confirm you've locked the doors isn't long enough to fire the compressor too trigger the air horns, but I can live w/ it for the rest of the benefits.

I got mine at Harbor freight for only $18 which is a pretty good deal.