Lifeguards at our local pool make $8-10/hr and would have either equal or more training and responsibility than a babysitter for one child would have - IMO.
I have paid up to $10-$13/hr but with economy what is, I think it's time for the babysitter bubble to burst a bit and get more affordable. This is what I would pay for 2 kids:
13 yr old - $5
16 yr old - $7-$8
19 yr old - $8-10 (I would pay on the higher end for a weekend night for an older girl)
We have a mother's helper who is 12, and will help with the kids while I'm home. Her mother said to pay her $3/hr - so I'll do that.