Applications of inertial measurement units are extremely diverse, and are expected to see a further increase in number due to current trends in robotics as well as recent advances in Micro Electromechanical sensors (MEMS). The traditional method of inertial measurement has depended on costly, power-intensive, error-prone Inertial Measurement Units (IMUs) that represent a single point of failure. Promising areas of current research include methods for combining multiple redundant sensors, which collectively provide more accurate and more dependable estimates of state, and wholly new IMU layouts that seek to reduce error. New types include: gyro-free, timing, wireless, distributed redundant IMUs, and IMUs that incorporate MEMS components for miniaturization in general. This review paper highlights these new research directions and lays out the design and experimental implementation of a complementary filter for inertial measurement.