There are several options out there, but I rediscovered an old standby, the National Geodetic Survey's VDATUM tool.
Here are some of the other options out there:
- ENVI/IDL - the BCAL Lidar plugin is a great tool if you have ENVI, but it only handles horizontal coordinate transformations.
- ArcMap - in the version 10 world you could import LAS files to LAS dataset and reproject, but that still leaves the raw LAS file in its native projection.
- ERDAS 2014 - has a define/reproject tool, but it's not very transparent.
- LP360 - can reproject LAS files, but the $ for a licence was outside our scope.
One of the great things about VDATUM is that it is platform independent (PC, Mac, etc.), since it's just a lightweight Java program. It does both horizontal and vertical transformations from and to all the major datums/projections, as well as quite a few lesser known ones. VDATUM has an excellent user guide so I won't go into the details.