software recommendations - Thinning large LiDAR point cloud?

I have a large point cloud (LAS file) and I am trying to thin this using a complex technique. I know it is possible to thin a point cloud using simple techniques such as extracting every n_th point. However the point cloud I am working with is more dense in some areas and less dense in other areas. I would like to be able to thin the cloud so that the denser areas are thinned more heavily than the less dense areas. To do this manually one could create a grid and select certain number of points within each cell. (ie one at each corner and one in the center) However this point cloud is much too large for this task. I am trying to figure out if there are any existing solutions to this problem such as a complex selection query, other automated process, or existing software application that could be used.