http://www.nature.com/news/2010/100518/full/465276a.html
NASA hopes to certify Falcon 9 or Taurus II (or another commerical rocket) by the end of 2013 for planetary missions. Falcon 9's successful first launch helps that process. Hopefully, they will fill the perfect-sized shoes that are empty once Delta II is finished after launching GRAIL next year. Perhaps the next Discovery mission, with a launch date in 2016ish, will be able to intiate the planetary program to these new launch vehicles.
Does anyone know of proposed Discovery missions that are baselining to Falcon 9 or Taurus II? The ones proposed to the outer solar system like IVO, TiME, or AVIATR still need an Atlas V or Delta IV I'm sure.