Splitwise - Splitwise is a free tool for friends and roommates to track bills and other shared expenses, so that everyone gets paid back. On the web, iPhone, and Android!
Splittable - Shared living made simple
Tricount - Manage and share expenses with friends
/Tab - The simple way to split a bill among friends.
Kittysplit - The easiest way of sharing costs with a group of friends
Roomr - Discover great people to live with