Yves Saint Laurent's Teint Parfait Complexion Enhancer is one of the those products (rather like YSL's Touche Eclat) that I always have at least three of (one in the bathroom, one in a purse, one in the drawer of my desk). There isn't much more to say about it really, other than it simply works: it really does enhance the complexion - as in you look like you, but somewhat more presentable.
You can wear it over foundation, in which case you miraculously look like you aren't wearing any. Or on its own. I usually take it neat, not being a big foundation person (except for days when I am an emotional wreck and have the self-esteem of a jilted 17-year-old). Teint Parfait is really more of a highlighter than base or foundation; it balances out the the skin tone, warms you up and looks natural.