This summer, the new Terminal 3 opened at Cancun International Airport.
As far as I can tell, all US airlines and some European charter flights arrive here, so there’s a good chance this is where you’ll end up. Terminal 2 (the original terminal that all flights used to come through, which is divided into two separate wings) still handles all domestic flights, and a random selection of international flights: Air Canada comes in here, as do some American Airlines flights from Miami.
In Terminal 3, there’s an ATM just after customs, but it wasn’t working when I was there (Oct 31, 2007). There’s also a money exchange desk right there.
Transport desks are just down the hall, on your left as you’re walking toward the doors. The desk for buying ADO/Riviera bus tickets to either downtown Cancun or Playa del Carmen is the last one on your left. Just a note: it looks like the downtown Cancun bus doesn’t come to Terminal 3–so you just hop on a Playa bus for the short ride over to the other terminal (this is what happened to me).
But there is a dedicated shuttle van between the two terminals–it runs every 20 minutes. You can also walk between the two terminals, though it’s not advisable with a lot of luggage. The walk looks a little dodgy–you feel very “behind the scenes” for a little stretch–but it doesn’t take long. In Terminal 3, head left along the front of the building and basically keep heading straight; from Terminal 2, turn right and keep walking, past the bus depots.
(If you’re wondering whatever happened to Terminal 1…well, it’s still shut, and basically never used for commercial flights. Just pretend it doesn’t exist.)