There's a small office in the train station, but the main office is located right when you get off the vaporetto at the San Marco stop, in a stone pavilion wedged between the small green park on the Grand Canal called the Giardinetti Reali and the famous Harry's Bar. It's called the Venice Pavilion/Palazzina dei Santi (tel. 041-529-8710 or 041-522-5150; www.turismovenezia.it; vaporetto: San Marco) and is, frankly, often more interested in running its gift shop than in helping tourists. It's open daily from 10am to 6pm. They've kept open the old (and just as indifferent) office under the arcade at the west end of Piazza San Marco at no. 71F, on the left of the tunnel-like street leading to Calle dell'Ascensione (tel. 041-529-8740; vaporetto: San Marco). It's open Monday to Friday 9am to 3:30pm. During peak season, a small info booth with erratic hours operates in the arrivals hall at the Marco Polo Airport.
The tourist office's LEO Bussola brochure is useful for museum hours and events, but their map helps you find only vaporetto lines and stops (it's well worth buying a street map at a news kiosk). More useful is the info-packed monthly Un Ospite di Venezia (www.unospitedivenezia.it); most hotels have a handful of copies. Also keep an eye out for the ubiquitous posters around town with exhibit and concert schedules. The classical concerts held mostly in churches are touristy but fun and are advertised by an army of costumed touts handing out leaflets on highly trafficked streets.
The city's official tourist-board site is www.turismovenezia.it; the official site of the city government (also full of good resources) is www.comune.venezia.it. A couple of good privately maintained sites are Meeting Venice (www.meetingvenice.it) and Doge of Venice (www.doge.it).
The Museum Pass grants admission to all the city-run museums over a 6-month period. That includes all the museums of St. Mark's Square: Palazzo Ducale, Museo Correr, Museo Archeologico Nazionale, and the Biblioteca Nazionale Marciana -- as well as the Museo di Palazzo Mocenigo (Costume Museum), the Ca' Rezzonico, the Ca' Pesaro, the Museo del Vetro (Glass Museum) on Murano, and the Museo di Merletto (Lace Museum) on Burano. (Note: The Lace Museum is closed for renovations until 2010.) The Museum Pass is available at any of the participating museums and costs 18€ for adults, 12€ for students under 29. There is also a San Marco Musuem Pass that lets you into the museums of St. Mark's plus one of the other museums. It costs 13€, and 7.50€ for students.
Venice, so delicate it cannot handle the hordes of visitors it receives every year, has been toying with the idea of charging admission to get into the very city itself. Slightly calmer heads seem to have prevailed, though, and instead we have Venice Connected (www.veniceconnected.it), which started in 2009 and gives discounts if you buy tickets through the website before arriving. You can get tickets for everything from transportation to museums, but you must do it for a particular day that is at least 4 days in the future. In return, the city gets, at least in theory, a better idea of how many people will be in town on a given day.
Also, for tourists between the ages of 14 and 29, there is the Rolling Venice card, which is something akin to the Venice Connected discounts for students. It's valid for 1 year, costs just 4€, and entitles the bearer to significant (20%-30%) discounts at participating restaurants, and a similar discount on traghetto tickets. Holders of the Rolling Venice card also get discounts in museums, restaurants, stores, language courses, hotels, and bars across the city (it comes with a thick booklet listing everywhere that you're entitled to get discounts). Year-round, you can pick one up at the Informagiovani Assessorato alla Gioventù, Corte Contarina 1529, off the Frezzeria west of St. Mark's Square (tel. 041-274-7645 or 041-274-7650), which is open Monday to Friday 9:30am to 1pm, plus Tuesday and Thursday 3 to 5pm. July to September you can stop by the special Rolling Venice office set up in the train station daily 8am to 8pm; in winter you can get the pass at the Transalpino travel agency just outside the station's front doors and to the right, at the top of the steps; it's open Monday to Friday 8:30am to 12:30pm and 3 to 7pm, and Saturday 8:30am to 12:30pm.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.