yeah, it seems every day i have to take off a rounded and/or completely rusted up bolt off(i do up old bikes)....First i'll just tap it to try and loosen it up with a hammer and give it a spray with WD40, if that doesn't work, i'll try heating it up a bit with a mini blow torch, that sometimes gets things moving....then, if all else fails, i'll get an angle grinder and grind a slot so i can hammer a heavy duty screwdriver anti clockwise to try and unsrew it.....
This has only not worked once, i ended up having to cut it off with a hacksaw blade, make sure you get a sharp one, not like me who was there for half an hour working on the bloody thing..