For many American workers, just thinking about the damage done to their retirement accounts since the beginning of 2008 can be painful. It has gotten worse lately as turmoil in the U.S. financial sector has sent worldwide markets into a tailspin, dragging hundreds of billions of dollars invested in retirement plans along for the ride. So what can you do to stem the flow of any more money out of your 401(k), 403(b) or 457 plan?