From the great online Smashing Magazine, an old post (but a goodie) on combining typefaces in a layout. An interesting table rating type combinations for 22 commonly used typefaces.
“The fact that there are no hard and fast rules about combining typefaces can make the process of making good choices time-consuming and maybe even a little exhausting. But it’s also nice to have a handy set of principles, as well as an understanding of certain typographic situations to avoid, to guide the process as quickly as possible to a pleasant typographic result.”