For the GPSr-eTrex Legend. 8mb of memory, 1000 waypoints. If I'm correct, you can also get a palm program to transfer waypoints to the GPS, but I'm not sure.
I use the combination of a Zire 21 (I paid $60 for mine, I'm sure you can get them for less) and CacheMate. CacheMate costs $8, but it's WELL worth it. It'll hold as many waypoints as you can put in its 8mb memory.