Sita buses (http://www.sitabus.it) go along the coast from Sorrento to Amalfi and from Amalfi to Salerno. Choose the region "Campania" from the website to find the timetables. Tickets cannot be purchased on board but are very easy to find in bars, newsagents, etc. Many people opt to rent the ubiquitous scooters, which is a indeed a good option, if you have previous experience, otherwise the heavy traffic and narrow roads makes this a bad place to learn.
