GPUShark is a simple, lightweight (few hundred of KB) and free GPU monitoring tool, based on ZoomGPU, for NVIDIA GeForce and AMD/ATI Radeon graphics cards. GPUShark is available for Microsoft Windows only (XP, Vista and Seven). GPUShark offers a global view of all your graphics cards in a single window. More information HERE.
GPUShark can display for every GPU the clock speeds (GPU core, memory), fillrates, performance states (or PStates), GPU fan speed, GPU/memory/MCU usage and power consumption (NVIDIA).