Bolt Head Rounded off - How do I get it out?

Today I was trying to change the front brakes on a 2002 Ford Ranger pickup truck. One of the bolts that holds the metal frame which holds the brake pads has an extremely difficult rusted bolt. Penatrating oil didn't help and now a 6-point socket can't grip it without slipping off because the bolt head has rounded off. What can I do to get this bolt off? The bolt is in a part of the suspension where I can’t use anything but a socket. :banghead:

You can buy a tool to remove a rounded/rusted bolt that looks similar to a socket. I have a set made by Sears, the inside where the flats of the socket would be are 3-4 coarse spirals that pull the socket into the bolt head and allow it to grip a rounded head. I can't think of the name of them at the moment. Believe it or not they work quite well provided there's enough of the head above the surface.
Failing that, if you have access to a welder you can weld a nut to the end of the bolt and remove it that way....Mike

you may also try a pare of visgrips. it will damage the bolt more but should remove it, besides if its rounded of youll need a new one anyway!

I have a device like mmikey's. Mine is made by Erwin and the set has six sockets of various sizes. I've used it to remove a locking wheel nut (lost the key) and also a strip head oil drain pan. It looks exactly like the femal version of an "easy out". You simply position the socket over the bolt and tap it once or twice with a hammer. Then use your socket wrench to remove it. Since it is counter threaded it will only work to remove and not to screw in a bolt or nut.