The Greater Manchester Area is fairly well served by an extensive bus network with the addition of trams but there is also a free shuttle service around the city centre.
The Metroshuttle runs three lines coded by colour, orange, purple and green and they services all the main areas and attractions, also connecting the train stations (Salford Central, Oxford St., Piccadilly and Victoria for the MEN arena) and central coach station in the city centre. The shuttle is free and the stops are signposted throughout the area. They run in one way circular routes about every 5 - 10 minutes, depending on the route. The website has a downloadable map for the routes and the site lists all the stops as well. I've used it several times and it's really convenient. Free is always good, too.