I stripped the head off a bolt rusted into the engine of my 1972 speed boat and after trying just about everything (including the pipe wrench method that usually works) I got a set of “Bolt Out” from Craftsman at Sears. It’s a kit I can now not live without.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=42263&item=4369654674&rd=1

This is the small set. It is what i have and gets the job done, but i would recomend the full set ($50.00 at Sears) I have wanted the in between sizes every now and then.