SiteTopo is a free surface modelling / contouring program to use with AutoCAD.

Loads survey point files, or DXF and XML formats.
Works with plain AutoCAD (no addons needed), and makes no changes to
your CAD setup.
3D view lets you see your survey from any perspective.
No installation, standalone executable.

http://www.sitetopo.com/

Flash movie of the program: http://www.sitetopo.com/flash/demo1/demo1.html