Livorno and Civitavecchia (outside of Rome). There are also ferries from mainland France and Spain to Sardinia, but these sailings can take as long as 12 hours. Grandi Navi Veloci, Moby Lines and ...
Moby Lines offers ferry services to Sardinia from various locations on the Italian mainland. In addition to Livorno, departure ports include Genoa and Civitavecchia to the north-west of Rome.