A recent study at Tel Aviv University revealed that as-yet-undetermined compounds in coffee actually prevent the development of bad breath. This totally seems contrary to us, having been on both ends of some pretty heinous coffee breath, and even the researchers themselves had originally sought to find the link between coffee and increased halitosis.
Their experiments revealed that three different brands of coffee had the same effect of slowing the growth of the bacteria partially responsible for stinky mouths. They also found that the gases released by the bacteria were significantly decreased, as well -- another component of bad breath. While they're not sure quite yet just what elements of coffee are contributing to this effect, they are continuing to study it in hopes of finding something that can be used in future breath fresheners.