Mine is also an excel spreadsheet, something similar to what WetAugust and Bananistheanswere has described, 12 different sheet for each month of the year, and on each year a list of what comes out (from column H, how much, and on what date of the DD for it comes out. I then have an extra column alongside it where I combine outgoing on a particular day so that if I have 2 items coming out on say the 11th then it totals up the 2 items and I can adjust each item as and when they need amending and that column automatically adjust via a formula.
This may sound a lengthy but below all this I then have columns A-E representing Transaction Date, Income, Outgoings, Balance and Funds Available (as I have an overdraft which I sometimes have to dip into.) Each row represents a day in the month, (so some sheets have 31 dates other have 30 or 28). I have a formula laid out that say D4=L4 (which is all transactions coming out on the 1st of the month.
I manually put into the income columns the amount that comes into my bank on whatever day it arrives, so the formula works out what my balance and funds available are for each day based on what income is and what outgoings are that day. Again anything that is outgoing, incoming say every 1 or 4 weeks (not quite monthly) I manually add it to the outgoing column as a + to any formula figure that is already there.
so formula on 1/3/12 under outgoing looks like =L4+44, this adds £44 onto the figures and just count down four thursdays and add the £44 to any figure (if there is one).
At the very bottom of columns and funds available I have a cell which is linked to the next sheet and so adjustments follow through to next month.
This gives me a daily account of where my bank balance should be and if I look up online banking i can see if I am deviating off at all and can forecast when money will be tight months down the line.