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!
iLend - Keep track of the things you lend and borrow.
Splittable - Shared living made simple
PayRequest - SImple Fast Payment Links
EquiTable - Split the bill fairly
PayPal.Me - Request money using your own personalized URL.