Arjan van Wijnen created a new real-time experimental OpenCL path tracer, called Laguna. It runs surprisingly fast and uses a seemingly new kind of grid-like acceleration structure (which the author calls a "precalculated blocks structure"). Something to keep an eye on.
Screenshots and executable demo at http://www.geeks3d.com/20120502/laguna-real-time-opencl-path-tracer/. You can change parameters like resolution, samples per pixel, number of bounces and grid size in the 'scene.txt' file.