I c/r against aggressive opponents with:

1) TPGK
2) two pair
3) air

I don't do it often, but I think you have to do it a little to keep people from picking off your c-bets.

I will usually call a c/r with TPTK and re-evaluate on the turn, but it's read-dependent. If it's coming from a tight player, I'll usually dump it.