Actually, WD-40 works pretty well for cleaning brake pad residue off rims, rubbing alcohol works, Simple Green works, acetone works, Coleman fuel (white gas) works, etc., Of course, once that's done the WD-40 should be cleaned off, but even if it's just wiped off leaving a little residue, it's not the big bugaboo a lot of people make it out to be. At least I haven't been able notice any difference. Just about the best thing I have found for cleaning the braking surfaces of rims is a Scotch-Brite pad and spit. Followed by wiping down with a reasonably clean (not oily) rag. For removing the glaze from the pads I like to do what neil0502 suggested and use a file.

One thing I have found out is that sometimes temperature will cause brakes to squeal. I had one set of $5 pads that would howl like a banshee when I first started my commute in the morning, but not do it later in the ride, or on the afternoon ride. All the cleaning in the world with different solvents and cleaners didn't help, toe in didn't help, flat pads didn't help, I finally figured out it was the temperature. Anything above the low 50's and they didn't squeal.

I like spit as a cleaning solvent, the price is right, you never discover you've run out when you need it, you never forget where you put it and it's never out of reach.