Locally, you can ask your art council if there are any annual or current benefits that they can refer you to. My city hosts a large Artists Against AIDS event where 40% or more of all sales go to AIDS research.
For those that sell on EBay, Mission Fish is a well known portal for listing charity auctions. You can donate 10% to 100% of your sale to any of the 9,360 nonprofit organizations registered with the site. Because Mission Fish has everything set up ahead of time, there is very little work involved in getting your funds to your chosen charity.
Art for Healing collects work and distributes it to hospitals, children's homes, hospices, retirement homes and other healthcare facilities. They take both donations of art and money and are open to learning about other facilities that would benefit from their organization. This group is located in California.
The Art Connection places donated art with the public, charitable, and educational institutions that could not otherwise be able to afford it. This group is located in Massachusetts and has a great section on setting up your own local art donation program!
http://www.artforcharity.net/>Art for Charity will display your work in one of their online galleries for potential buyers. After your work has sold, 10% of the sale goes to the organization and at least 33% to a charity of your choice.
Art 4 Charity is a UK organization collaborating with 29 charities and projects to help both people and wildlife nonprofits. Contributing artists offer all or most of the sale price to promote the supported causes.
Donating artwork not only benefits the charities you are supporting, but it brings your work in front of a new audience that might not otherwise get to see it. In doing so, you are both promoting your own career, and breathing new life into the art culture we all strive to enhance.
Consider gifting a little of your time and your work this year! If you know of other causes and organizations, please share them in the comments.