DEM

A Portal to High-Resolution Topography Data and Tools OpenTopography provides an end-to-end system for the distribution and processing (DEM generation) of LiDAR topography data. KMZ files for LiDAR-derived images

The MapWarehouse allows you to purchase and download GIS data instantly using a simple Google Maps interface. Purchase orthophoto, parcel, base maps and DEM

Whitebox GAT is an open-source and transparent GIS and remote sensing package that is flexible and powerful. This is the replacement for the much-used Terrain Analysis System (TAS).