Visit York promotes York tourism. It has information about venues, can book hotels and B&Bs (no booking fee) and has tickets for events (right-hand room from main entrance).
They also have free bus timetables, and handy maps, including the official York Cycle Map (in the corner display of the section on the left).
Current details of guided tours are also here.
If you need information about current special events and entertainment, both the office and their website are a good source of information
A few books (such as the guide to the Snickelway walks) and selected York and Yorkshire souvenirs are also on sale in their small shop.
Tip The office sells the York Pass, a good way to cut down entrance costs if you visit several places during your visit. Do check out the information carefully, however, because, though convenient, it may not be the most economic way for you to pay entrance fees.