I have a garmin vista cx, it is small and sometimes hard to read but it tracks, has waypoints, can take a fair size memory card, is usb, color screen, 2 AA's last 12 hours or so, has compass and altitude........
The only thing I'd change is to have the high sensitive receiver. Came out just after I bought mine. Once and a while if you're cruisin' down the road and the trees are close it looses signal. I beleive the ones dedicated for vehicles have the high sensitive receiver to deal with urban cover.
I'd make sure what ever you end up getting is usb (which they should all be now) can take a memory card, can load the maps you want and has the high sensitive receiver.