scarepigeons?

:D

give them popcorn.

KaiN hit it on the head. Get a Cat. Pigeons hate cats.

try to hung some unwashed undies.

stool pigeons

alka seltzers do wonders on seagulls. Try it on a pigeon. :)

eastpak: doubt his neighbors would appreciate that.

You don't really need a predator to scare them away - just a predator's scent. You can buy canned urine for several species at most outdoor stores - I would start with that. We used to use bear piss on our deck in my parent's old place to keep all the annoying aviary type creatures away.

I've also been told that reflective metallic objects (spoons, streamers, even the insides of pop cans) will drive them away...although I don't have any direct experience with this one.