I've been asked for this many times from budding cooks. How do you know that pears go with walnuts or browned butter goes with sage. Why does honey go with duck so well and how do I know that mint will work well with lamb? Someone made a graphic over at Information is Beautiful that shows this. They don't link up ALL the great connections (the aforementioned lamb and mint aren't on there and they don't pair duck with orange which is classic) but it's a good start. Enjoy.
Here's a pre-view. To see the entire thing click the link above.