I'd suggest either the Etrex Legend HCx (£150) or the Etrex Vista HCx (£170, with added barometer and electronic compass). The built in base maps are indeed fairly useless, so you will need extra maps of some sort.
Options are:
a) City Navigator on micro-SD card £50 per large country (UK & Ireland, France & benelux, Spain&Portugal etc
b) City Navigator on micro-SD card £80 for full Europe
c) Mapsource Metroguide Europe on DVD £113
d) City Navigator Europe on DVD £140
prices from
http://www.gpsw.co.uk/relitems.html?ProdID=3550
(not sure why the CN Europe DVD isn't listed - it's on the search OK).
The SD cards will be copy protected, so no backups, and also you may not be able to log your rides to the cards so you'd return with a fairly crude log of where you'd been (eg no times/heights logged).
The DVDs can be used on your PC for planning, and you can write as many micro-SD cards as you want. The cards can only be used with your GPS though. You can also leave space on the card for recording for rides in full detail. I've got UK, Ireland, France, Spain, Portugal and adjoining parts of Belgium, Germany, Switzerland, Italy on a 1GB card, with about 100M free for data logging at ~3MB per day, 1sec interval.
Metroguide officially doesn't do routing on the GPS, where it should just be a background map. There is however a data fix from a chap in the Netherlands that allows the routing data that Metroguide uses on the PC to be included in the data transferred to GPS/card. Google MetroWhizz or MetroGold.
All of these will include all roads for the UK, France, Germany etc, subject to very recent changes and a few errors. Some countries may be less complete (eg Greece).
It is difficult planning off a small GPS screen, and I'd be reluctant to just tell it to take me to the next hotel 50 miles off, so I'd recommend taking some larger scale paper maps, like the IGN 1:250,000 series, for route planning.