I just got a Garmin IQUE 3600 and am learning about it. Here's a forum where you can find out a lot of good information.

http://www.pdastreet.com/forums/forumdisplay.php?s=fe1cf9109d21026de0ef9ae43d3baa89&forumid=108

The following programs seem to be mentioned a lot in terms of topographical programs….

Fugawi
Pathaway
GPSPilot
easygps
ozi

I’m also in need of an app like you mentioned. I’m currently leaning toward Fugawi but really know nothing at this point.

All I do know is that so far I am definitely NOT disappointed with my Garmin IQUE 3600.