Each year, the U.S. tax code seems to grow in complexity as existing rules are amended or new rules are implemented. As taxpayers, we know these changes can mean a fatter refund... or an unexpected bill come tax time.

This year is no different. The tax code is constantly in flux, and moves made for 2009 returns are likely to leave some taxpayers cheering and others in disappointment. The following changes to the 2009 tax code are likely to have the largest impact on the greatest number of people, for better or worse.

1. Deduct the Sales Tax on a New Car Purchase -- With Fewer Strings Attached. You were able to deduct the sales tax on a new car purchase in years past, but you also had to itemize your deductions to do so. Since about 2/3 of taxpayers don't itemize, this has left many individuals out in the cold when it come to this tax break.

For this year's return, you can use the sales tax paid on a vehicle to increase your standard deduction. The end result is that you get the sales tax break, even if you don't itemize.

There are a few rules to keep in mind. The car must have been purchased after February 16, 2009, and the amount that can be deducted is sales tax imposed on the first $49,500. As well, the credit begins phasing out if your adjusted gross income is less than $125,000. At $135,000, no deduction is allowed.

2. The Homebuyer's Tax Credit Applies to More People. Most people know about the tax credit for new homebuyers. But there were recent change to the credit that opens it up to more individuals.

First, the income cap has been raised for first-time buyers. The full credit is now available up to a cap of $125,000 for single filers or $225,000 for joint filers (previous caps were $75,000/$150,000). After that mark, the credit is phased out.

Second, the credit is also expanded in the form of a 'long-time resident' credit. Homebuyers that have been in their previous homes for five consecutive years out of the last eight are available for a credit of $6,500 on the purchase of a new home.

3. Lower Standard Mileage Rate. If you drive your car for business, you won't be able to deduct as much for mileage this year. In 2008, the IRS set the standard mileage rate at $0.505 per mile. But amid soaring gasoline costs that year, it raised the rate to $0.585 in the second half of the year.

The 2009 rate has decreased slightly to $0.55 per mile, meaning you'll get a smaller deduction this year than you had in 2008.

The 2010 rate has been decreased even further, dropping to $0.50 per mile.

4. A Higher AMT Exemption. Originally designed to ensure the super-rich paid their share of taxes, the alternative minimum tax (AMT) has gradually snared more and more taxpayers. In 2003, about 3 million taxpayers had to file using the alternative minimum tax. This year that figure is estimated to be 35 million.

For those having to pay the AMT, it sometimes comes as a shock considering that the alternative minimum tax equates to higher taxes versus using the traditional tax code. But there is some relief. The exemption amount for the AMT has risen to $46,700 for single filers and $70,950 if filing jointly, meaning more income is sheltered from the tax.

5. A $400 Tax Credit for the Majority of Taxpayers. Although it applies to the bulk of taxpayers, there seems to have been little buzz about the 'Making Work Pay' credit.

This credit is equal to 6.2% of earned income, up to $400. The credit does get reduced for earners making more than $75,000.

The best news about this credit is that there is no special process for receiving it. If you file using a tax preparer or tax preparation software, they will automatically include the amount. If you prepare your taxes yourself, you only need to fill out the Schedule M form to receive this extra cash.

Are you interested in getting more tax season tips? Click on these links to view additional tax-time articles from InvestingAnswers: Top Tips for Avoiding an Audit in 2010 and 10 Ways to Make Tax Season Less Painful.