Banana:
As others have said, take the time to peruse through the forums here, and you will find lots of information. Once you have done this, the decision-making tree for selecting what type of GPS you should by goes more or less like this:
1) Do you want your GPSR to be able to "autoroute" you to your destination, or simply show you where you are at present?
Autorouting is great if you plan to tour mostly on public roads in areas that you might not be totally familiar with. If you plan to spend all your time in an off-road environment, autorouting is not that big an advantage.
2) If you choose autorouting, there are four Garmin models that support this (I'm not familiar with other manufacturer's products). These are the GPS V, SP III, and SP 2610 or 2650.
a. The GPS V is inexpensive, small, has batteries in it for handheld use, has a black and white screen, and can hold a limited number of maps - 21 megs worth (about what you need to hold the City of London).
b. The SP III is a little bit more money, bigger, has batteries in it but really is not suitable for hand-held use because of its weight and short battery life (caused by the colour screen), and can hold up to 128 megabytes of maps (pretty much all of the British Isles on one load).
c. The SP 2610 is the newest model, much faster calculations than the SP III (think Pentium 3 compared to 486), colour, does not have batteries (which means it is only useful in a car or moto, where you have 12 volt power), and can hold up to 2 gigabytes of maps, which is sufficient to hold all of North America or all of Europe at one time.
d. The SP 2650 is the same as the 2610, but it has internal electronic gyros that enable it to continue to accurately track the position of the automobile (not motorcycle) when the satellite constellation is blocked from view by buildings, trees, tunnels, etc. It's really meant for use in "urban canyons" - downtown in big cities.
Personally, I think a decision on an autorouting model should be made between a GPS V or a SP 2610. The SP III is kind of "old technology". If, however, your budget is limited, you could consider getting a USED SP III - there are some good bargains to be had on eBay. Just make sure you buy a unit with a European basemap, and the eBay seller includes the European map CD with all regions unlocked and the appropriate unlock codes to use the CD with the GPSR.
If you're over 40 years of age, the GPS V is not really the best product to get, because the display is pretty small and you need razor-sharp near vision to interpret it. Past 40, we don't change focus from infinity to 50cm so fast anymore - so the bigger display and addition of colour on the SP III and SP 26xx is a big help.
3) If you don't need autorouting, there are many very small and inexpensive GPS models that will show you where you are, and show major roads and highways. Go shopping for these at any big electronics store.
If you need help/advice about an eBay purchase, just post a link to the auction here, there are lots of folks on this BB who are very knowledgeable about GPS who can look over the auction goods and tell you if there is anything missing or anything to be concerned about.
PanEuropean
or if you need to get to street level in say London 
