I would raise with 2-2 3-3 4-4 or 10-10 J-J Q-Q K-K or A-A. I usually leave the middle pairs alone as they most often just seem to get me into trouble. Also, most people won't expect you to be holding a very small pair, so you can often get these players to at least call one more bet. If I am ever re-raised though, I would usually fold the small pairs (unless you feel like re-re-raising). If it is a nolimit game, I'd raise fairly big with the smaller pairs, and about 4-5 times the big blind for the high pairs. Just my 2 cents worth though.