Have you seen billmonk.com? This is what I use currently to keep track of tabs with roommates. BillMonk was bought by OgoPay in 2007 though and since then they haven't changed a thing on the site.
Check out Mr. Moneybags! It's cool.
It currently is cumbersome to enter in multiple debts simultaneously (i.e. splitting a big check). However, we're developing this functionality now and are excited to debut it.