Only thing I can think of is a GPS sleeve for a PDA. PDA costs extra.

I reckon that learning how to read a map properly is a better idea anyway. You'll learn much quicker when you are challenged to think about it rather than just watching a pretty arrow on a gadget.

One hint is to color copy and laminate areas that you intend to use - an A4 section folded in half to A5 will easily hold a 50 mile round circuit route. Obviously, keep the full map in a backpack just in case you decide to (or accidentally) leave the laminated portion. Many people get bothered with the unfolding and refolding of the map so neglect to look at it until they are well and truly lost - having a small laminate helps avoid this situation.

Another hint is to make sure that you have a compass handy. On a bike I'd use a small handlebar mount compass. Get into the habit of glancing every 100yds or so (or anytime you change direction). Soon you will build up an instinctive knack for knowing in which direction you are travelling, and also for being able to remember direction changes that you have made in the past mile or so. This _really_ helps when you get the 'uh-oh' feeling as you can recreate on the map where you really went from your last known-good position.

Of course, there is room for GPS in all of this - many GPS receivers have a "UK Ord Svy" datum that will give you your instantaneous location in the format that you can look up directly on the map.