I use 89 for my car (87 isn't good unless you have a four-banger; I have 281 cubic inches of displacement to feed
)and that's running about $3.48 in Pittsburgh. Best part is I only get 7-12 mpg in my car.
While on the topic, I told other people this (and not to stump speech, but put a jab in). I think $4 gas will motivate Americans to start considering use of other fuels. I think once a gallon hits $4.50, it's never going to go back down. (Google "Peak Oil" and you'll see what I mean). If they can create a decent way of using CNG for cars, you won't have to ever worry about shelling out $100 a tank like some in California are doing right now
Natural gas just doesn't have enough octane in it to make a decent engine, plus it only gets about 1/3-1/4 of the supply, so you can't go cross country with it. But I will say this (especially in PA): With the Marcellus Shale fields being tapped, you're going to have dirt cheap natural gas, drilled in America by Americans, and shipped literally out of your backyards, by American companies whose land is owned by Americans. A win-win situation, if you ask me.