Meguiars clay bar, and their Quik Detailer product or any "quick detail" spray on product. (in between wax detailer)
Good Luck! Those spots are a b!tch to remove. I've used a light abrasive pad (kitchen cleaner sponge pad) some Armor All wheel cleaner, and some good 'ole elbow grease to remove the spots.
'01 E430, Sport 72,000 mi
'98 C280, 126,500 mi