Here's a couple I have bookmarked from my early GPS-ownership days. Check Yahoo Groups too (http://groups.yahoo.com/). You'll find a number of GPS-discussion groups.

http://gpsinformation.net/

http://www.gpsworld.com/gpsworld/

http://www.gpstm.com/ //free GPS software//

http://www.easygps.com/ //more free software//

http://www.gps-practice-and-fun.com/

http://gpspassion.com/

http://members.shaw.ca/davepatton/gps.html

http://forums.groundspeak.com/GC/

http://www.edu-observatory.org/gps/gps.html

Dan

Edit: If you've already bought a unit, consider buying an after-market instructional DVD for your specific unit (exist for many mainstream makes/models). Helped me immensely - made the user manual make sense, and a whole lot more fun. Don't remember if I got mine at Amazon or at my local Sportsman's Warehouse.