detailers clay is what you need.
if it were oxidation then the clear coat of paint would discoloured though.. hopefully it isnt a bad paint job where bits of dust and stuff have settled on/in the clearcoat before it dried completly, in which case it'll need a wet sand and then some cutting/polishing work.
if its just surface contaminents (sap, raildust, tar etc..) then you have a few choices to make. autogeek.net has a nice online selection of car care products including clay. make sure you plan out your lubricant also.. some ppl use a solution of car wash and water to **** while claying, others use specialy sprays. you can probably get stuff locally also.
after claying try putting your hand inside a zip lock bag and then feel the finish of your car. any imperfections will stick out like a sore thumb using this method.
good luck! and post some pics if you can (before/after clay and wax stuff)