Send a free Mother's Day e-card and they will donate $1:
http://www.toasttomom.com/home.html(had a widget for blogs, but didn't seem to work here)
Last Christmas, they had a similar deal - download a holiday song free and they'd make a donation.
If you enjoy similar things - Care2.com will connect you to many click-a-button for charities. And check my del.icio.us for the game FreeRice.