When I first moved from England to North America one of the things I found hard to get used to was getting paid every two weeks instead of monthly. This means that some of your bills are monthly, some are biweekly, and occasionally I had more or less money than I expected as they got out of sync.
I've been using a simple elisp program I wrote to let you manage your upcoming bills, weekly budget items like groceries, and your regular income. It runs through a period of dates you supply, and a list of incomes and expenses, and produces a csv file and a buffer that contains the output of the forecast. It shows the highest and lowest balance of the period too, so you can spot if you will go over drawn, and also see peaks when it's a good time to move money to savings.
The code is hosted on google code as emacs-easy-budget and is also released as GPL v3. Hope somebody finds it useful.