Here you can find links to software that you can download for free, including GPS, GIS and Remote Sensing programs:
http://www.spatialhydrology.com/freedownload.html
Two blogs with lists of free GIS software:
http://veryspatial.com//?page_id=559
http://mapzlibrarian.blogspot.com/2006/06/my-powerful-geospatial-suite-of-free.html