If you donate stuff to a legit charity or other qualified organization, then you may get a little kickback from the government come April 15. It'll mean a bit more work on your tax forms, but you -- and the people who got your unwanted but still useful possessions -- will all benefit from those few extra minutes. Just ask the diligent folks at H&R Block.
Anyway, the key is to save any records from the donations. Then when the grueling process of filling out your taxes rolls around, you'll have everything you need to document how awesome you were at helping others throughout the year. Check the IRS Web site to find out which forms you need to fill out. More on that in this article: 10 Tips for Getting the Biggest Tax Refund.