What's a good Canon 7D ND Filter for daytime?
 

I purchased the Canon 18-200mm lens for daytime shooting. It's actually pretty good lens (for daytime, horrible for nighttime).

I'm looking to keep a shallow DOF during the day w/ this lens: So, what would you recommend? Anybody use the Colkin drop-in filters? What ND's would u recommend? Is that the way 2 go? P-Series?

Is there a better option?

I like the variable ND filter I got from here:
Light Craft Workshop - Fader ND filter (ND2~400)

Goes from 2 to 8 stops with a simple twist. Fairly cheap for the convenience as well - you can keep a wide open aperture in most outdoor conditions.