ScottishHills.com – An amazing resource covering all Munros, Corbetts, Grahams and now marching its way through the Marilyns
Walkhighlands – loads of detailed walking routes.
The Mountains of Scotland – Marilyns, HuMPs, Donalds, Tops – a great hill locator.
mwis – my weather bible
Geocaching.com – A great resourse for finding local info and walking routes you might not have known about.