Flights. Kayak is indispensable for travel planning because it can search for the best deals across multiple airlines as well as on online travel sites such as Expedia, Orbitz, Priceline, and Travelocity. Search for round-trips or multicity itineraries. Flights on domestic airlines and discount carriers may need to be booked through the individual airlines. Some domestic airlines offer discounts for in-country flights to travelers who fly with them for their international travel, and many are part of global frequent flyer alliances. For some domestic carriers, you may need to search for and book flights from their websites.
Lodging. Most flight-booking sites also reserve hotel rooms — although they don’t typically include budget hotels, hostels, and bed and breakfasts. For hotels, Trip Advisor is a comprehensive site, with listings and reviews of thousands of places around the world at all price levels. You can sometimes book a place through Trip Advisor, but it also has links to sites where you can make reservations, which may be cheaper. (Trip Advisor now does flight searches, too.) Reservation sites include Booking.com, Hotels.com, and Lonely Planet’s booking service — the latter is great for reserving specialty places, such as traditional ryokan inns in Japan and guesthouses in Southeast Asia. For budget places and hostels, try Hostels.com. Want to stay in someone’s home? Try Airbnb.
Transport. Train passes can be a great value, but they typically must be purchased before arriving in the countries that offer them. Buy Eurail train passes through Eurail.com; several authorized agents online sell Japan Rail passes. For buses, consult current guidebooks for the names and Web addresses of bus companies operating in the countries you plan to visit. Be warned, though, that many countries have a bewildering number of bus companies — often with their own stations in the large cities — and it can be difficult to make reservations online. Bus companies with websites typically provide timetables and prices, although these may not be reliable.
In addition to these resources, search online for city guides — many of them free — and public transportation maps. Consult embassy websites for answers to questions about passport and visa requirements. The XE Currency Calculator provides current exchange rates.