The space shuttle Discovery sits at Kennedy Space Center waiting for repairs to be made to its fuel tanks after a crack in the foam insulation around the tank was discovered and a subsequent investigation found cracks in some support structures on the fuel tank. A piece of foam falling from the tank is what contributed to the fatal accident when the Columbia broke up while reentering the atmosphere in 2003 killing all seven astronauts onboard the spacecraft.
NASA is working on a fix for the fuel tanks and investigating what caused the cracks. The shuttle fleet is set to retire permanently in 2011 and the Discovery is set for launch on February 3 at this point, though NASA is considering whether the launch needs to be delayed to wait for repairs.
After the Discovery launches there will be two or three more missions and then the US will catch a ride aboard Russian spacecraft for trips to the ISS moving forwards. NASA is also looking to the private sector for cheap ways to get to the ISS.