Nintendo's (NTDOY) Wii Sports Resort, a game we were already expecting to be one of the biggest sellers of the summer, just got even more attractive.

Nintendo announced this morning it will bundle the "Wii MotionPlus," a snap-on attachment to the Wii's wand-like controller, in with the new Wii Sports game. The device promises to make the Wii's motion-sensing controls far more accurate.

Nintendo is basically giving away the MotionPlus: The Wii Sports Resort-MotionPlus bundle retails for $50, average for a game (hits stores July 26). And Nintendo will also sell the unit separately for $20 starting June 8, a price far lower than we're used to for videogame accessories.

We're not sure how much the device will add to existing Wii games, but already a few third-party titles like EA's (ERTS) Grand Slam Tennis (coming out June 18) will explicitly use MotionPlus.

It's a fantastic strategy for Nintendo. Especially if MotionPlus proves to work with older games, we think Wii owners will turn out in droves to buy the new Wii Sports and pick up the device. The move also raises the bar for Wii competitors the Xbox and PS3 -- with Nintendo putting out new features for its console at low cost, both Microsoft (MSFT) and Sony (SNE) will be on the defensive all summer.

Source Business insider