2009, a bond maturing in 2010, and so on, out to perhaps 2013. When your 2009 bond matures, you’d extend your ladder by buying a bond maturing in 2014.
This technique offers double protection. If interest rates fall further, you’ll be ahead of the game because you’ve locked in some of today’s yields for periods out to five years. Alternatively, if rates rise from their 2008 lows, you’ll have bonds maturing each year, to reinvest and reap those higher payouts.