LiDAR, if you work in GIS and pay any attention to digital elevation model (DEM) data, you have heard of LiDAR. Although many people know it has something to do with bouncing light off terrain and it is very accurate, many times knowledge ends there. Fortunately there is an outstanding resource for learning about LiDAR.
The USGS put together this very well organized resource. Although it focuses on applications of LiDAR for natural resources, over 75 percent of the lesson focuses on data collection methods, factors of accuracy and other technical aspects of LiDAR applicable to anybody who uses LiDAR data. Fully narrated with animated visual aids it is a great resource, one I highly recommend.