Garmin eTrex Venture
You might also look at Magellan's SporTrak GPS ($170; www.magellangps.com), which has memory and features similar to the Venture. A little sturdier case, perhaps, and some people may find its interface easier to use (that's more a matter of personal taste than anything objective).
If you opt to spend a bit more, then the Magellan SporTrak Pro ($270) has enough memory to support detailed internal maps in addition to the usual collection of waypoints. Or, Garmin's eTrex Summit ($229) incorporates an accurate compass and altimeteran excellent choice for mountaineering, cross-country skiing, and backpacking.
Hope your son enjoys his gift!