For an entirely new flavor, try out Thai Coconut Peanut m&m's. I'm not sure they agreed with my sensibilities of delicious, but they're something different from the rest of the vast m&m's line. The coconut and peanut make a robust flavor combination, with a lot of savory mixed with the sweet. I'd be curious to see people's reactions to these.
As for the flavor vote: British Toffee has my heart!