If you don't use an impact, you can use a 1/2" drive breaker bar (preferrably with a long pipe extension for added leverage). There's a special tool you can buy to brace the crank pulley to keep it from spinning (IIRC, they can be found on ebay or google search) - or you can have a friend crawl under the car and lock up the TC so enough pressure can be applied to break the crank bolt free.

As Jake mentioned, make sure you use a new crank bolt (they're one-time-use stretch bolts), and make sure you torque it to spec (150 ft/lbs, PLUS a 90 degree turn).

Good luck! Makes a big difference in the power output - you'll definitely feel it