I found this free 3-D LiDAR LAS file viewer PointVue LE from GeoCue Corp., which can be downloaded from this link.
The free viewer provides you the capability to view only a single LAS file at a time in 3-D. It allows you to color the LiDAR points according to elevation, intensity, classification, return number, and source id. It does not have the capability to render the LiDAR points as surfaces or as contours though. There is also no way to cut a cross-section profile view of the data.
It has some basic functions to display the LAS file header and generate some statistical information about the data as shown below.
If you are looking for a simple LAS file viewer with reasonable visualization performance, PointVue LE may be what just you are looking for.