You lose all of your weapons/perks/etc for an extra custom class slot at every odd prestige, for example 1,3,5,7, and 9 for a total of 10 custom classes. You unlock new backgrounds for your playercard, new prestige game modes, new icons, gold camo at prestige 14, new emblems, and lose all of your cod points.
Heres a link in case i missed anything
http://callofduty.wikia.com/wiki/Prestige_Mode#Call_of_Duty:_Black_Ops
