Revocation of privileges, extra chores, writing lines, being made to do nice things for elderly neighbors, etc (with your supervision)..doing volunteer work. Giving up of their time, since they are wasting yours with the sassy back talking. Discussing with them if they like to be talked to that way...ask them if there are teachers, older kids on the bus, other adults in their life who don't value their opinion, or let them speak those opinions...if so, then they know what it is like to be talked to in a way they do not like. It has to start somehwere to make change.
I am honestly disturbed by all the replies that support corporal punishment....spanking, washing mouths out with soap, vinegar, soy sause.....really? What does this teach them? That you are bigger and can bully them?
I was raised in an era where some of this stuff occured.....very very rarely. Respect was taught. Step back..have a plan so you are not just lashing out and reacting.