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Correct me if I'm wrong, and if I am, I'll eat a nipple.
In cultures where bare-breastedness is the norm, women (nor men) aren't particularly sexually sensitive about the nipples. If you don't feel any erotic sensation about your own nipples, do both of you a favor and say so; or experiment with pinch/tongue/nibble/rub/slow/rough/silk/etc. play until you find something you like. I would give my front teeth (well, maybe just the crown) for a lover to play with my nipples until they were sore. =)
Ice! How could I forget the pleasures of ice? (go easy, frostbite != erotic) Hot wax? That's a bit on the xtreme side, not for everyone.