Scotland is famous for walking and climbing and perhaps the most famous walk is The West Highland Way. There are four of these official long distance walks and the map displays all 4 of them.

Here you will find their offical websites:

The West Highland Way
The Southern Upland Way
The Speyside Way
The Great Glen Way

And for shorter (even more quiet and private) walks/climbs you can always check out the most informative website for nice walks for beginners and experts.
Bev's Favourite Walks in Scotland

My personal favourite walk is:
Beinn Eighe Mountain Trail

Do not forget to check out the Picture Gallery on Beinn Eighe & Loch Maree, The Skye Walk Website and Undiscovered Scotland for all other walking and climbing links

And the most wonderful website of all for those interested in Munro's with every Munro listed with all details and picture: Munro Magic