I believe I've mentioned this product before, but I want to make a blog post specifically for Clarins Instant Smooth Perfecting Touch. It's one of the best products I've personally used for covering up oily skin. It's not amazing, but it works better than just about any other mattifying product I've used. I still get some shininess breaking through after a couple of hours, but it's better than nothing.
However I did discover that this stuff works particularly well when combined with Milk of Magnesia. Neither Milk of Magnesia nor Clarins works particularly well on its own, but the combined effect of both really impresses me. I apply a layer of MoM and leave it on for 15-20 minutes. Then I get my fingers a little wet and wipe off the remaining white streaks. Next I apply the Clarins, and then I'm good to go. That keeps my shine down significantly for several hours.