Fuji Velvia 50 - it is the standard by which landscapes are measured.

I am starting to work with the new Velvia 100, but haven't formed an opinion of it yet. A good alternative to Velvia is Kodak VS100. When shooting the color landscape, as someone has already pointed out, pay attention to the light and how it "flows" across the landscape. Velvia does the best job of enhancing the warm light, which has the add effect of bringing warmth to the image. As an aside, it would be good for you to also get an 81A and 81B warming filters, as well as 1 and 2 stop split neutral density filters.