Most major tourist services are clustered around Parque Central. The square has three different banks with ATM's.
There's a tourist information bureau on the north side.
The post office is just west of the plaza, on Calle de la Plaza just behind the archeology museum.
Internet cafes are plentiful, but don't expect a fast connection. Wifi service is difficult to find. There is a plan in the works to turn all of the Parque Central area into a hotspot, but at this point the service remains unreliable. Inquire in ViaVia for details. The B'alam Cafe (see Restaurants section) does offer free and somewhat speedy wifi service to customers upon request.
One thing that can be difficult to locate is a pharmacy. There's a good one on Calle Independecia, across from Twisted Tanya's.