Besides sweet, salty, bitter, sour, and umami, yet another taste has been found and researchers said that it would be likely to find even more in the future.
The taste is fat. Yes, fat. Researchers had been debating on whether fat is a taste or not for half a decade, and according to Newsweek, they decided. Purdue University, after much speculation concluded that fat is not only a taste carrier (carries and amplifies taste), but a taste all its own, meaning that receptors on the tongue pick up the prescence of fat as one of the elemental tastes.
This is likely the reason why french fries, meat, potato chips, and the like are so tasty— they have a taste all their own (this research comes hot on the heels of another study that found that the taste of fat will cause people to synthesize fat within their own bodies— just tasting cream cheese will cause one to gain fat!). This knowledge may be used to explain why fat-free versions of food just don't taste as good and may help us eventually find ways to improve fat-free food.
Sources:
http://www.sciencedaily.com/releases/2001/12/011204073223.htm
http://www.cfs.purdue.edu/html/alumni/spr2002/tasteimprovement.htm