I am considering a cold chisel and split the nut. I also found another one I like which is drill a hole in the side of the nut and fill with penetrating oil. I have never tried that. I think it would take too much time.
I have not been very successful with the nut/screw extractors. I never was either until I started using the ones like I pictured and I haven't had a failure yet since I changed styles.
One more method question. What about smacking the bolt a few times and cutting off above the nut. I would worry about the cast snaping when I was smacking the bolt. [/QUOTE]
Pictures of what you are dealing with would help us help you.