DD2 bit me a few times when she was getting her bottom teeth. It was usually at the end of the feeding, so I tried to really pay attention to when she was done, and unlatch her before she could bite. I would also say "ouch," and frown. You just don't want to react too dramatically, if you can help it. Otherwise, it can make them reluctant to nurse for a bit. She hasn't bit me since that little phase, and it's been several months.
You can also say, "ouch, the hurts mommy," and set them down for a minute. Then try again a few minutes later.
Here are tips on dealing with biting from kellymom.com: