| Candy maker Clarence Crane, wanting to branch out from chocolates, saw a pill machine being used to make round pills in 1912. Since most available mint candies at the time were square, round mints were a novelty, and a hole could be punched in the middle to make them even more different-looking. The name came from the resemblance of the candies to the doughnut-shaped life preservers used on ships when a person had fallen overboard.
But despite their origin as mints and the (now-deleted) writeups focusing on those flavors, Life Savers now come in about 25 flavors. The most common (at least everywhere I've lived) is the Five Flavor pack (orange, pineapple, cherry, lemon and lime); packages are also available of "Five Tangy Flavors," "Tropical Fruits," "Wild Sour Berries," "Butter Rum," "Wild Cherry," "Hot Cin-O-Mon," "Chill-O-Mints," "Wint-O-Green," "Pep-O-Mint," "Cryst-O-Mint," and "Spear-O-Mint." Apparently it's only the "Wint-O-Green" that spark when crunched in the teeth.
Sources:
http://www.ideafinder.com/history/inventions/story005.htm and http://www.candystand.com/LifeSavers/ | 
