There are a few ways to estimate your refund...
If you're good at math, you can print out a form 1040 from the IRS and throw your round numbers in to see what comes up. Tax geeks like me do this.
If you're trying to avoid math altogether, try some of the free estimation tools available from tax pre sites.

Two of the more popular are H&R Block (http://www.hrblock.com/taxes/tax_calculators/index.html) and Turbo Tax (http://turbotax.intuit.com/tax-tools/calculators/tax_estimator.jsp).

You'll want to have some basic tax information handy, such as your filing status, dependent info, income from wages and investments (including capital gains and losses), expenses and deductions (including mortgage, charitable contributions and taxes). Don't forget records of withholding and payments made during the year.

Plug in the numbers and you should have a good estimate of what to expect.