Now here is an automated Expense Management System Gyaati.com, which has been developed based on Web 2.0 concepts and open sourcing. The whole system is developed keeping in mind the needs of people who are sharing expenses aka accomodation but find it difficult to maintain and track the expenses. The system solely works on Social Networking (Or Can we term as Partner networking), where each and every user would register to the site and form a group (People who are sharing the expenses) in the same.
Any expenses by any one in the group, would be sent as a email notification to the other member of the group, for their approval. Once the Transaction is approved, the monetary transfer would be performed in person by the group members. Site provides the group members with tracking, based on approved, approval pending. And ofcourse a tab to Create aka logging in the expenses. One person, can be a part of many groups (One for accomodation sharing, One for Car pooling, one for Weekend Outings etc etc.). The expense sheets and data would be available only for the members of the group. Atmost care has been taken for even transaction types. Like equal splitting or different expense split among members. The second one usually comes in Hindu community when some members of the group have Non Vegeterian and some not.(Usual Problem I face :)) ). The other feature includes leaving messages for partners. Remember the stickies on the walls.
UPDATE : Recently I came across better and more sophisticated way of doing same thing on Bill Monk. Check out various options. I am sure you are going to love that site.