I think it's easier to wear an illuminator over your foundation -- but if you need a luminizing foundation, try NARS Sheer Glow. The finish is by no means iridescent, but it is luminous: http://www.sephora.com/browse/product.jhtml?id=P24
If you need a good luminzer, I recommend the NARS Multiple in Copacabana or Luxor (http://www.sephora.com/browse/product.jhtml?id=P28
What I do is use the primer first then the foundation. I use the luminizing lotion on my nose, cheekbones, forehead, tip of my chin and the philtrum (the indentation above your lip) and my temples after foundation and before I set it with powder.
Usually if you are looking for a illuminating finish, you can mix an illuminator or a luminizer with your foundation (benefit high beam, girls meet pearls, moon beam, Nars orgasm illuminator and many others). But if you particularly want a illuminating foundation, then the only one I know is Stila Illuminating liquid or powder foundation. I have never used it, but my friend had tried it, and she wasnt a big fan of it, I guess its a hate it or love it thing.