I find the best thing for me is to keep a spreadsheet where I track all of my spending and bills. I tried using quickbooks, but I didn't like it so I created a spreadsheet.

I keep track of my bank account, but I also have my monthly budget on it. Every time I make a purchase I add the amount to my bank balance spreadsheet, but also to the budget spreadsheet. The budget spreadsheet shows me how much I've spend on whatever category and automatically tells me how much I have left to spend on that category for the month.

The budget spreadsheet also has all my bills in it do I can see whether I have paid them or not.

I go online to my bank's website every day and highlight the things that have posted to my account, so I will know if I missed something or if I forgot to mail the check etc.

I'm rather obsessive about it, but its the only thing that works for me. I would be totally scattered if I didn't keep the spreadsheet. When I was relying on a checkbook the book would constantly be lost or I would forget to add things, and I would be overdrawn all the time.