The Colorado and Oregon series have some that come pre-loaded with Garmin's topo maps, IIRC.

Personally I've used many GPS units in the eTrex line and the 60Cx model. The 60C(S)x series is great & tough, but a little bulky. I went ahead and changed to an eTrex Vista HCx for the space savings.

Garmin offers units pre-loaded with mapping software, or you can buy it on a memory chip, or else buy the CD/DVD and manually load the maps onto the GPS unit of your choice.

You definitely want one of the Garmin units with a "high sensitivity GPS chipset" so you can get a better satellite lock in iffy areas (forest, canyons, etc.).