For colour landcape I use Fuji Velvia 50 and Kodak E100VS, as Mark stated they are very saturated films (VS is for Vivid Saturation) but I like the results, expecially in the Colorado Plateau, and I don't find the colour so unrealistic, but it's a matter of taste )))...
On the other hand I don't like Provia, it seems to me that lacks "personality"...
A lot of people are satisfied with Velvia 100, some say that it covers a territory between Velvia 50 and Provia 100, but I never tried it so I can't articulate about that...