Despite what Gary says, don't use WD-40 on your cams. It attracts dirt and removes oil which lubricates them. Then you have to use more Wd40, which attracts more dirt. Eventually your cam seizes up completely.
Instead, the best thing you can use is "White Lightning" bike chain lubricant. If you can't get any, Metolius Cam Lube is the same product in a different bottle at a higher price