I agree with the excel recommendation.
Set up it up so that you can enter in your monthly income and expenses. If you use mint, it can help greatly for categorizing things.
For example, you could have a Bills category, with sub-categories for Electricity, gas, phone, internet, etc. You can use mint to get what you spend on average for each of these categories, etc. etc.
I take mine a step further and have setup a cash-flow forecast to see how money goes up and down with time. I can do what-if scenarios, where I can see what happens to my "net checking balance" over time if I were to for example increase my monthly grocery bill by $x a month or make a one time large purchase. I then keep track of my checking balance to see if it follows what I have forecasted. I find that so far, I have followed the forecast fairly well, so this helps me plan out when I can make lump-sum investment contributions. For example, I try to keep my checking balance above a certain minimum...and then when it goes above $5,000 said mark, then I take that amount out and put it into investments (e.g. Roth).