ProShares UltraShort 20+ Year (TBT) is an ETF that moves inversely with US Treasury bond prices. In other words, if interest rates rise then you make money. I think it's getting harder (although not impossible) to envision a future in which we won't have substantially higher interest rates. Might be a worthy add to portfolios if you're concerned about this.

BTW, watched I.O.U.S.A. this week (http://www.iousathemovie.com/). If you want to have the crap scared out of you about the impending issues with the debt that's the movie to watch.