Hitchhikers.org, brings drivers with empty spaces in their cars and in need of some laughing, a serious conversation or a (small) compensation, in contact with people looking for a ride.
Change the language settings at the top of the page (in the right corner).
Road Sharing, autostop and carpooling for commuters, free car sharing and hitchhiking service.
blablacar (probably the most used car sharing site within Italy). A car sharing platform making travel within the UK and Europe cheaper, greener and more fun! Also offers an overview of the national carpooling services and websites.
Backseat Surfing, Score ultra cheap city trips/ Share a carpool appointment/ Make money on the trip you were going to take anyway