I use Quicken to track all of my expenses. I bank online via Quicken also (as opposed to my bank's online banking feature.) I don't use cash for anything (I use a debit card) and thereby have an electronic trail of where every cent goes since all of my bank transactions load automatically into Quicken to a predetermined category. It's great because you can run reports that detail exactly where every cent goes, can compare categories from month to month, can setup budgets and then track variances etc.
I manage money for a living so all of this is really second nature to me. But you don't have to be a financial person to use this software. I have helped many of my friends get set up in Quicken for their personal use and they have told me months later that they don't know how they ever managed with it.