I used to track all of my upcoming expenses in a spreadsheet. I had it nicely laid out and colour coded to make sure I knew what the state of all my accounts would be given the projected upcoming expeditures.
Eventually I got fed up with all the manual copying and pasting, inserting new rows, fixing the formatting, etc. That's when I started flophase to replace the spreadsheet. It just gives me the basics at this point but it has all the functionality that my spreadsheet had and more already.
It keeps track of historic transactions as well as upcoming ones. It can handle many accounts and multi-account transactions as well. More interesting features will be coming as I get time.
The basic idea is you have a list of transactions that affect one or more accounts (chequing, savings, credit card, etc). As you enter the data, the balances of the accounts are updated in real time to show you the expected state after you pay your bills or buy that new TV. As time passes upcoming transaction become historic. You just need to update the balance of the account to reflect the actual balance and the expected balances are all updated automatically.