Export-oriented companies (or funds) are another.  If the dollar tanks, many American exporting companies should do relatively well, as our huge trade deficit begins to right itself.

Some gold seems prudent, as a bet, but I wouldn't go overboard on it.  Shifts in gold holdings by central banks (ours, for instance, if things get really shitty) can make this a tricky market.

In really bad times, such as the coming likely period of stagflation, cash is king.  Pay off debts, liquidate most long stock positions, shorten up bond investments, and hold safe cash instruments.  Downsize living expenses wherever possible, before you're forced to do so involuntarily.