I found this new open-source software CloudCompare for 3D point cloud and mesh processing, which comes along with a light weight viewer ccViewer. The interesting thing for LiDAR professionals is that the viewer is compiled with support for reading and displaying LiDAR LAS files. The display performance is pretty good even for large LAS files, but that's just about it for the viewer, other than some basic viewing perspectives and basic display coloring. It only has the ability to color the LiDAR points by classification or by elevation. On the other hand, the source code is available and if you have the time and the inclination, you can fork or contribute to the project and make the software work better with LiDAR LAS files.
To run the software, simply double click on the ccviewer.exe executable extracted out from the downloaded binaries as shown below. Note the presence of the libLAS.dll in the extracted folder.
This should open up the ccViewer application window.
Now all that is needed to display LiDAR LAS files is to drag and drop the file onto the ccViewer application window.
The following prompt might appear but simply click OK and the LiDAR point cloud will be displayed.
http://www.danielgm.net/cc/, where the binaries and souce code for the CloudCompare and the ccViewer software can be downloaded.