Is the car an auto? If it is don't ride the brakes! We get this alot at work with auto coupes, what happens is that when you continually ride the brakes the pads get glazed and become really really smooth and constantly squeak. Check the pads for glazing, they'll look really shiny, if they are shiny pull out a flat file and file the surface till the glazing goes away, alternatively you could just use some emery tape to roughen up the surface, but make sure the surface stays even.
Also as other people have lready suggested, chamfer the edges and use CRC anti-squeal. Works like a charm for us at work, goodluck with it!
Phat Drift Damaged
Cobalt Blue 1994 EF XR8 5 spd
Fully optioned - Sunroof, cruise, body kit
Stock as a Rock for the moment