Canada, Mexico, a few random others. Most use 220, little bit more efficient in transmission, otherwise no real difference.
Edit:
Ask them what it uses. Devices all have stickers that show their required input voltages/wattages. If it's a higher end device like a laptop, rechargeable camcorder, usually it'll be dual-voltage, like 110/220, so it'll work anywhere in the world, just need a new cord.