Something I really like doing is free charity stuff. It only takes a moment of your time, and you can do it once a day. Just click on the buttons on the following websites:-
The Hunger Site
The Breast Cancer Site
The Child Health Site
The Literacy Site
The Rainforest Site
The Animal Rescue Site
Sign up to any of the above to give even more!
South American Rain Forests
Homes Of Endangered Species
U.S. Wilderness
Coastal Habitats
Reduce Pollution
Sign up at the Ecology Fund and they'll save even more!
Care2.com also has a whole load of them, and if you want to keep track of how much you're saving, register with them. They also have really fun eCards which are free to send and also generate money for charity!
And here are a load of random ones I've found over time:
Clean up your country
Save rainforests
Save rainforests (German)
Plant a tree in a Brazilian rainforest
Plant an oak tree
Plant a tree in Niagara
Help the environment
Fight poverty twice a day
Fight hunger
Help pay for an operation
Help to cure cancer
Give one minute of health care
Help education in developing countries
Help children in Argentina (click the GRATIS button)
Raise awareness of climate change in Greenland
Provide clean drinking water (click the 'doneer gratis' link, then put in the four letters and click 'doneren')
There are a couple of comprehensive lists of them here, here and my favourite one is this one.
Another good way to donate is by using one of these search engines:
SearchKindly.org (Works in conjunction with Google so it's my favourite!)
TheEnvironmentSite.org
GoodSearch.com (uses Yahoo! Search)
CharityCafe.com
You can also use this search engine once a day and sign up with them to make sure the money you generate goes to the charity of your choice!