Garmin Edge 205/305/605 - there might be some others too. Forerunner is good, big wrist watchy thing.
What you're after is a mapping unit. Colour or B&W, you download your maps onto the unit and follow your pointer on the screen.
If you buy Memory Map software, planning your route is a snap - just download to your GPS and off you go. On the other side of the coin, anywhere you ride can be recorded via your GPS, uploaded as a tracklog to Memory Map on your laptop or pc and saved as a future route. You can also 'fly' the route via the software - neat!!
If you buy a non mapping unit, you'll get your directions as vectors on the screen with a pointer to follow. You'll still need a map ideally, but if you have the Memory Map software, you can plot your route, print out a map with just YOUR route on it (for cross reference) and follow the vectors on screen, referring to your back up map (A4 sheet) if you need to. You can still download your plotted route to your non-mapping GPS unit and upload the tracklogs.
The Edge models are good cycling specific units and offer other functions as well - HRM, cadence, crank speed and the usual performance orientated stuff.
I want one!! Amazon.co.uk do the Edge 205 from £100
and the 305 from £162
There's a wealth of extras available - USB cables, serial cables, extra antennae, etc.