Ask HN: How do you track your personal expenses?

My girlfriend tracks our expenses for each month on a piece of paper as follows:

  amount, location, category, date, payment method
  $50, Whole Foods, food, May 19th, MasterCard
  $19, taxi, transportation, May 23rd, Visa

At the end of the month, she adds up the amounts for different categories and payment methods. It's a bit of a chore to do it manually. I know how to process this with a text file, but I'm wondering if there are any good iPhone apps that will do this. Failing that, a simple browser or cross-platform desktop app. There must be something but I have no idea where to begin. I don't really want anything more complicated than what I've described. Quicken or whatever the heck is too complicated, I would rather try and hack something into Excel.