According to About.com, a 1946 nickel's value depends on whether it was minted in San Francisco or Denver and whether it has been circulated. A 1946 nickel that hasn't been circulated is worth between $2.20 and $2.80.
A 1946 nickel that has been circulated is only worth its face value. After 1945, production of nickels from a nickel-copper alloy was resumed, severely reducing their worth. Nickels from before 1946 and after 1941 were made using a silver alloy, which made the nickels 35 percent silver. These partially silver nickels can be worth anywhere from a few dollars to a few hundred dollars depending on circulation and rarity.