Ray and I have been working on an app that started from a hackathon for a few months now. It's called Budgie! It's currently available for the App Store if you have an iPhone. Android coming soon for those droid users here.
Every day you get a daily allowance and that's what you get to spend per day. You can spend more than your allowance but then you go negative (bad). Every day you get your allowance (at 12am your time) and anything left unspent rolls over to the next day. You make money by not spending it!
I've been using it just to see how much money I spend on an average day and I have to say at first the results were genuinely surprising. I've since reduced the number of things (or how much I spend) per day as a result! I find the allowance total gives me a good idea of how my "take-home pay" is being used and if it's been used effectively or not.
Try it out, and please leave any feedback here (or email us at firstname.lastname@example.org)!