If you're planning to blitz the sights, the Campania Artecard is an excellent investment. A cumulative ticket that covers museum admission and transport, it comes in various forms.
The Naples three-day ticket (adult/reduced €21/12) gives free admission to three participating sites, up to 50% off on others and free use of public transport in the city.
Other handy options include a seven-day 'Tutta la Regione' ticket (€34), which offers free admission to five sites and discounted admission to others in areas as far afield as Caserta, Ravello (Amalfi Coast) and Paestum. The latter does not cover transport.
Cards can be purchased online or at participating sites and museums.