One of the more obvious play with the U.S. dollar is to invest in commodities. That can be done through futures, funds and stocks linked to raw materials.
A commodity index fund is another great way to invest in commodities over the long haul, which will continue their bull run overall once the demand for infrastructure materials resume from countries and companies spending more money.
No matter what happens to the U.S. dollar though, which will obviously continue to lose its value, commodities will continue to rise based on the demand from growing middle classes in emerging markets.
So while commodities are a great play against the weakening U.S. dollar, they are also a terrific plays in and of themselves based on demand and supply; along with tight credit markets.