Becca has great primers, @Katiekost. Since I use a matte foundation, I prefer a primer that isn't as matte (since that can make me overly oily). My favorite is the Backlight Priming Filter.
The Becca works wonders for me, use sparingly so you don't get white cast. Also before primer, I spritz UD de-slick and pat it on my skin. All primers seem to work better for me doing that. Primers with silicones in them (e.g, many of them) will also cause foundation to slip on oily skin.