The Kepler mission will obtain high precision, continuous lightcurves for more than ~150,000 stars over the next four years. Prior to primary mission operations, ten days of commissioning data were obtained for the ~52,000 brightest targets in the Kepler field. While Kepler's main goal is the discovery of transiting low mass planets, it will also provide a rich dataset for studies of variable stars. These commissioning data give a first glimpse of the amazing diversity of stellar variability Kepler will observe. Here, we discuss the tools we are currently developing to quantify variability in the Kepler data, and show initial results on the distribution of target stars in these metrics. Ultimately these measures will be used both to characterize the data and to select active rotationally modulated stars for rotation period determination.