Assuming you're getting more than a paltry entry level bike, you'll probably need only a 4, 5, and 6mm allen wrench, a tire pump, about 15-30 minutes of time, and a little bit of patience in adjusting the brakes and derailleurs. Other than that, you probably won't need ANY additional tools other than maybe a 15mm wrench for attaching your pedals - assuming they don't have a 6mm female end at the end of the spindle.