The sawtooth instability is the most fundamental dynamic of an inductive tokamak discharge such as will occur in ITER. The sawtooth occurs when the current peaks in a tokamak, creating a region in the center where the safety factor is less than unity, q < 1. While this instability is confined to the center of the plasma in low pressure, low current, large aspect ratio discharges, under certain conditions it can create magnetic islands at the outer resonant surfaces and it sometimes sets off a sequence of events that leads to a major disruption. Under some circumstances the reconnection following the sawtooth is observed to be complete, but in other conditions it is incomplete. Sawtooth behavior is complex and remains incompletely explained. The SciDAC Center for Extended MHD Modeling (CEMM) has undertaken an ambitious campaign to model this periodic motion as accurately as possible using the most complete fluid-like description of the plasma -- the Extended MHD model. Both the NIMROD and M3D codes have been applied to this problem, and our Center is using it also as a non-trivial test problem to compare these two codes far into the nonlinear regime. The multiple time scales associated with the reconnection layer and growth time make this an extremely challenging computational problem. The most recent M3D simulation used over 500,000 elements for 400,000 partially implicit time steps for a total of 2x10^11 space-time points, and there still remain some resolution issues. However, these calculations are providing insight into the nonlinear mechanisms of surface breakup and healing. We have been able to match many features of a small tokamak and can now project to the computational requirements for simulations of larger, hotter devices such as ITER. These simulations form the basis for more complex phenomena such as the effect on these modes by an energetic particle component (such as produced by the fusion process), and the effect of externally generated electromagnetic waves (RF) on these modes. [This is the primary goal of the SciDAC Center for Simulation of Wave Interaction with MHD (SWIM)]. These calculations have been greatly facilitated by numerous interactions with the Applied Math and Computer Science groups, particularly with the TOPS group in optimizing the sparse linear solves, and the graphics groups in providing state of the art graphics capability.