Current source for CREE XLamp XP-G
I would not advise driving the led directly with household voltage - it is far too high for this low voltage device. A further consideration is that the led requires DC to drive it and the household power is AC.

These LEDs will draw 800-900mA at a forward voltage of around 3.2 v. If you use a wall wart (plug and voltage regulator all in one) with an output of 5v DC (a common value) then a 1.8 ohm 2 watt (or greater wattage) resistor in series with the led would do the trick. Note the led will need a heatsink as it will need to dissipate about 3W.