Not really enough info here:
Do you want it to autoroute?
Do you want it for navigation away from the bike?
Just to give you some things to think about.
I mostly know Garmin, but there are other choices.
If you are willing to make your routes on the computer (or slowly on the GPS screen), you don't need autorouting to follow a pre-planned course. (cheapest option)
Autorouting does allow you to divert from the shortest (or fastest) path, then when you want to get to your destination, it'll figure it out for you again.
Garmin does one map for all of Western Europe.. but it's not all that complete for some bits of Scandinavia. My City Select 6 map only has a bit of Finland... But all of Norway and Sweden. My Metroguide 4 only has a bit of South Norway and Sweden... (they both do Denmark) later versions may have more detail.. but the Maps cost quite a bit too.. if you are thinking second hand, you may not have the cash for newer maps.
I use a Garmin 60c, which does autoroute, and even autoroutes on the base map (the one hardwired into the unit), but my experience of using this map for routing is it sucks. The 60C with the City Select map does everything I need though. Mounts to my bicycle, rides in my pocket, mounts to my dash. The only thing I will miss (when I get a bike =) is that I won't hear the beep that it gives when a turn comes up.. I hope to work something out for that though... I don't need voice directoins as I glance at the screen when It beeps and see quickly what I need to do.
In short when you think GPS for bike navigation use, remember that beside the cost of the GPS, you need to buy a map product, you likely need a power connector (my 60C goes for a couple days on rechargeables, but the vibration from the bike I rented last month caused it to shut off.. by shaking the batteries, a power connector would solve this), you need to mount it.
Al...