Wii Sports which comes with the console will keep you occupied for a few weeks, especially when you try and reach targets and take the fitness test!
With Mario on the horizon its worth checking that out, theres actually two games coming out, Paper Mario and Mario Galaxy.
Then theres the much talked about Resident Evil 4 which is due next week. As well as Resident Evil : Chronicles which is more or an arcade shooter.
Then theres games that are already available such as Zelda : Twilight Princess which looks stunning!
It looks like you're planning to buy one at the right time as theres a few games coming out soon.