I like this idea: tax big banks

The idea is to levy a tax against large banks that goes up as they get bigger. The argument is this: when banks become "too big to fail," the government may have to step in to rescue these huge institutions (as we've just seen, unfortunately). And the tax, if passed on to these banks' customers, might encourage those customers to move to smaller institutions which are less likely to destabilize the whole economy with any bad bets that they make. More here.