With Gastus you can manage your expenses with concepts and several types. I’ve understanded that concepts are a kind of tags. Types are a kind of categories. I made it anyway like this.
Gastus shows you your expenses in several diagrams and flipcharts. In fact, there are two of this graphics. A cookie diagramm and a line diagram 
I’m testing it for this month. I think its a useful web 2.0 application to manage your expenses. It displays you how many money you expensed to which kind of category. Try it!
An API exists also for Gastus. I spent a little look to the API. Check out which functions are available!
Update:
Gastus supports now Apple’s iPhone! Take a tour.
Another thing I wouldn’t use, because of one simple thing: it’s on the web. And you are giving “them” some, for most people very very very, personal data.
Yes that’s a good exception. But in Gastus you don’t have to add your earnings. You only have to add your expenses. I’m only adding my expenses for my employer like lunch or drinks and so on.
Your content is very interesting, bookmarked
regards khhudf