I am very happy with the Garmin GPSMAP 60CS, which has a great color screen, awesome battery life, and can accomdate both road maps with routing and auto-re-rerouting as well as the topo maps. I have not used any topo maps yet, but it is comptabile. This unit also has 56 MB, which is on the large side for GPS memory - meaning you can load both some topo maps and regular road maps.
I think this is a great unit for hiking, biking, and driving. It is also waterproof and very tough - I have dropped it while bicycling over 30 mph twice and it is barely nicked and still functioning.