I can spend entire half-days at a time in Stanfords, may be worth a trip to London or Manchester if you're planning a serious trip?
You can spend a lot more than time in Stanfords
good online too. To give you an idea the next paper map i want of Norway is over £30 delivered.
There is usually good online mapping for most countries and its great for planning purposes but on the ground you want paper + maybe any GPS stuff you might have.
I have a garmin GPS but its strictly back up. Garmin do have very good coverage now but i dont think their topo maps are as good as the OS standard. SATMAP Active 10 are starting to look more appealing with good mapping coming on stream for Europe. Anyway you didnt ask about GPS systems but they are worth considering as garmin for instance allow you to use the maps on your desktop too in their basecamp software.
Do you have a destination in mind?