i can recommend Topo! although the interface leaves quite a bit to be desired. once you know how to work within it, you can do some cool stuff.
it's easy to trace a route on the topos, and then print out maps to take in the field. it's also dead easy to put in GPS waypoints and upload them to your GPS. i traced my whole Sierra High Route track into it, along with key waypoints (passes, lakes, trail in trees where there was going to be snow, etc.), and loaded them into a Garmin Geko 301.
the easily-generated elevation profile can be helpful too. as can the 3-D "fly thru" of the route. of course, google earth can REALLY give you a sense of what things will look like ahead of time too.