|Tips for Tipping Abroad|
Central & South America - Typically hotels and restaurants add a service charge, if not, 10% tip is a general rule for good service.
Europe - Service charges (or value added tax = VAT) are typically included in bills and on purchases. Make sure to read the bill carefully, because in touristy areas the tip can sometimes be hidden or hard to recognize, causing you to leave 10-15% extra on top of what might have already been included.
Asia/Pacific - Special care needs to be taken in this part of the world. In Japan, for example, tipping is often considered rude, though tourist-specific services, such as a tour guide, will commonly accept gratuities. China is another non-tipping society, though nicer hotels and restaurants will include a service charge in your bill. If you feel the need to tip, do so discretely.
Middle East/Africa - This region can be a bit more complicated. In general, tipping is very much appreciated and never considered rude, but tips are generally in small denominations and always in the currency of the country in which you're traveling.
My advice - If you can afford to take the trip, don't be stingy on a tip (unless you are somewhere it is considered culturally rude). Unlike in America though, 10-15% is often enough. If you'd like a more specific country-by-country list, check out Conde Nast Traveler's article on this same topic.