Quantum GIS (QGIS) is a user friendly, open source, cross-platform, and freely distributed GIS application. With QGIS, one can easily import multiple raster, vector, and GPS-like coordinate data for the purposes of geospatial data visualization, manipulation, and map production. For users seeking more advanced functionality, QGIS can also serve as a nice graphical interface to GRASS . For more information, read the release announcement  of version 1.7.
Online tutorials and demos
- How do I do that in QGIS?  (evolving wiki page, with additional links to video tutorials)
- QGIS GRASS Cookbook 
- Excellent QGIS tutorial materials  (FOSS4G workshop, 2007)
More on QGIS
- Software development retrospective  (Oct 2007)