The OEM shocks are actually pretty decent. The old saying of "you have to upgrade shocks when you use lowering springs" is not always true. In this case, the OEM shocks can handle a decent amount of spring rate. A big drop as others have said will cause problems because there is not a lot of bump travel...anything over an inch or 25mm is too much in my opinion for optimal handling and ride quality. We stuck with a 20mm drop plus we include replacement shortened bumpstops with our RCE Yellow springs.
Below is a shock dyno test we ran on the OEM dampers.
There is a lot to gain by going to Koni or Bilstein eventually (when they come out) but for most street drivers the OEM shocks will do the trick.