I just bought a Garmin Etrex Vista for about $200 (on sale). Haven't taken it riding yet, but it works great for hiking and in the Jeep. Garmin also has other Etrex units with less memory for a lot less $$$. The topo map software is about $100. It's a bit outdated (I think a new update is due to be out soon), but works well enough.
Recommendations:
(1) Find a store that carries the units and play with them to see which user interface you like best.
(2) Most units are much cheaper online -- run a google search.
(3) Buy as much internal memory as you can afford! This seems to be the biggest limitation besides battery life.
Good hunting!!!