I've seen a lot of talk of disc brake squeal on this site and wanted to offer my experience. Disc brakes squeal because the pad is vibrating while clamping on the rotor. This can be eliminated, or reduced to minimal levels, by using the proper shims and using a good brake shim grease between each shim, between the pad and shims, and even between the shims and the piston. The grease absorbs and deadens the squeal by preventing the pads from vibrating. Thin even coats on each surface should do the trick.

So, before you spend a lot of money on new pads/rotors, do a little research to make sure you have the correct shims, get a good quality shim grease, and try cleaning and re-greasing them. You may be pleasantly surprised with your results!