I love my L-series lenses and the 70-200mm Ls are some of the very best zoom lenses ever made (those others mentioned don't even get close); however, at certain focal lengths on a crop sensor, you're just as well off with the EF-S lens. You don't use the full image circle of an EF-L, so you're paying for something that you may not need.
However, if video is your aim, then why not get the 5D MkIII and one or two L-lenses? That's a great video rig, only surpassed by Canons dedicated cine bodies.
Ls do retain their value very well. If you buy used, then you have almost not depreciation.