In the U.S.:
To quote IRS Publication 526 of March, 2010: “Generally, you can deduct your contributions of money or property that you make to, or for the use of, a qualified organization. If you contribute inventory (property that you sell in the course of your business), the amount you can claim as a contribution deduction is the smaller of its fair market value on the day you contributed it or its basis.” This is not tax advice, and special rules may apply, so please consult your accountant with questions.
Many companies also categorize any expenses related to donating goods to events as marketing cost. (This is an observation, not advice.)
In Canada:
We are in the process of assessing expansion into Canada, and we invite you to join our interest list to find out when we launch.