Bradshaw did have a big arm as did Bert Jones. Of course you have Elway, Favre always in the discussion and someone mentioned Cutler & Boller. I still think Jeff George had one of the biggest arms but my money would be on that monumental turd named JaMarcus Russell as the qb with the biggest arm.
Its insane to imagine someone throwing a ball 100yds.
I know he doesn't have the strongest but, my lord Vick makes the most effortless 50yd throws I have ever seen and most of the time on the run off of his back foot. I would really like to see him open up on one with full stride.