Something always seems to slip through even the best budgeting net. Either we forget small expenses, or we forget major categories. Automated online money-management software -- such as what Motley Fool partner offers -- makes tracking down your dollars a lot easier. As you take a closer peek, let's also look at some places your money may be going when it disappears like the socks in the dryer.

Transportation. It's easy to budget for the monthly costs of owning a car, such as fuel and loan payments. It's the occasional expenses that throw the budget for a loop. When it comes to vehicles, this category can be huge. It might include regular maintenance such as oil changes and tire rotations. Or it might include more expensive unplanned repairs or new tires.

Then there are driver's licenses, registration, and inspections, not to mention tolls and parking meters. Even if no single item costs you a lot of money, together they can add up. Throw in the occasional parking ticket, and this budget category could be completely busted every month. Go back through your records and add up your annual expenses to get a more accurate view of your spending in this area. Or you might choose to add extra money to this category, to give yourself a little cushion for those unplanned expenses.

Subscriptions. Anything you pay for only once a year has a tendency to get lost in the budget shuffle. You probably never figured your annual memberships, such as those for AAA, your local discount warehouse, or your bacon-of-the-month club, into your budget calculations. This list might also include professional dues or association memberships.

Although it may not cost much to have copies of The New York Times or Martha Stewart Living delivered to your house, the overall cost of subscriptions can add up if you read several magazines and newspapers. And don't forget about your annual computer costs, such as software upgrades.

Gifts. Let's ignore the holidays for the moment. If you're exceeding your budget in November and December, you probably know why. But even if you've gotten into serious budgeting mode and remembered to account for your holiday spending, you might have forgotten other gifts. Expand this budget category if you're a year-round gift giver.

Since there's no shortage of opportunities to lavish your friends and family at all times of the year, from birthdays to housewarming parties, this budget category can be particularly big for people in large families, with their endless parade of weddings, baby showers, and graduation ceremonies. Then there are the few random dollars that folks collect at the office for someone's retirement or departure party. Add greeting cards to this category if you're a devoted card mailer.

Travel. Anyone working from a budget might already have had the foresight to include vacation expenses. It's the less exciting travel or local trips that tend to be forgotten -- weekend trips to the beach, camping excursions, and the like. You might omit those obligatory trips to see family in far-off states, if you're busy daydreaming about how to spend your vacation savings. If you tend to be the type to wander away from home often, add money to your vacation fund for this kind of travel.

Personal care. Let's start this list with dry cleaning, a budget category that can seem small when you drop only a few things off at a time. Try to track your spending over three months to get a more realistic view of your average dry-cleaning costs. Add alteration costs if, like me, you've rarely encountered a pair of pants that don't need at least two inches cut from the bottom.

The personal-care category also seems to suffer from budgetary self-deception. It's fine to tell yourself you'll forgo the eyebrow wax and manicure this month, but you won't keep your spending down if you don't keep the promise. A new lipstick here and a few fancy soaps there, and this budget category can get bigger than you think.

Fees. This can add up to a sizable budget hole if you're incurring late charges, overdraft charges, ATM fees, and any of the other million things that banks charge you for these days. If you know you're a little careless with your spending, it might be worth your time to budget for these fees. If you start tracking your spending in this area, you might even start doing more to avoid them.

Cash. We pay for more and more of our daily needs with credit and debit cards, yet it's cash that seems to slip through our fingertips without notice. How many times have you looked in your wallet on a Friday and wondered what happened to the $60 you had there on Monday? Keep receipts for all of your cash spending for a couple of weeks, and see whether that solves the mystery. If not, keep a daily record of your cash expenses for a while.

Keeping these tips in mind will help you budget better. You may still have some hiccups in your budget here and there, but, hey, you can always budget for those, too.

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This article first ran on Nov. 28, 2006. It has been updated.

Fool contributor Mary Dalrymple looked for her budget under the couch cushions but couldn't find it. She welcomes your feedback. The Motley Fool has a full disclosure policy.