Impact tools are the cat's meow when it comes to removing stuck and even stripped bolts. Use one along with any of the other suggestions.
--any except Jassper's C02 suggestion. I'm not sure how you can use carbon dioxide (mehbe dry ice??) Care to elaborate Jasper?! (keep in mind I live under a rock) Also there is the risk that Gore will charter a 747 from his mining facility and then chase you down in a convoy of SUV's and ask you not to emit so much C02 if you try this technique
...I'm going to exhale on all my stuck bolts-nope, that didnt work. oh wait! my breath has desolved a bolt! oh sh-t! here comes gore! I better put my breath in a 'lahhhhck bahhhx.'