The all-day all-zone ticket is 10 Euro for one person. If you are going to be there for at least a couple of days, will be using the subway, trams or buses, and have more than one person, I've found the best deal is to get a 3-day 'Innenraum' partner card which covers up to 5 people traveling together in the inner zone (most of everything you'll want to get to) for 21 Euro. Then you also have to buy a partner 'Aussenraum' (outer ring) ticket to get up to five people from the airport to the inner zone (9 Euro). They don't offer a 3-day Aussenraum ticket so you have to buy another one for the day you go back. (Assuming you have been there less than 3 days or have bought another inner-ring ticket along the way.)