  We have conducted a deep ($15 \la r \la 23$), 20 night survey for transiting
planets in the intermediate age ($\sim 550 {\rm Myr}$) open cluster M37 (NGC
2099) using the Megacam wide-field mosaic CCD camera on the 6.5m Multiple
Mirror Telescope (MMT). In this paper we present a catalog and light curves for
1445 variable stars; 1430 (99%) of these are new discoveries. We have
discovered 20 new eclipsing binaries and 31 new short period ($P < 1 {\rm
day}$) pulsating stars. The bulk of the variables are most likely rapidly
rotating young low-mass stars, including a substantial number ($\ga 500$) that
are members of the cluster. We identify and analyze five particularly
interesting individual variables including a previously identified variable
which we suggest is probably a hybrid $\gamma$ Doradus/$\delta$ Scuti pulsator,
two possible quiescent cataclysmic variables, a detached eclipsing binary (DEB)
with at least one $\gamma$ Doradus pulsating component (only the second such
variable found in an eclipsing binary), and a low mass ($M_{P} \sim M_{S} \sim
0.6 M_{\odot}$) DEB that is a possible cluster member. A preliminary
determination of the physical parameters for the DEB+$\gamma$ Doradus system
yields $M_{P} = 1.58 \pm 0.04 M_{\odot}$, $M_{S} = 1.58 \pm 0.04 M_{\odot}$,
$R_{P} = 1.39 \pm 0.07 R_{\odot}$ and $R_{S} = 1.38 \pm 0.07 R_{\odot}$.
