My favorite organization to donate to is the MSPCA here in Massachusetts, and more specifically, to their Angell Memorial Hospital. Here's the link to their website:
http://www.mspca.org/site/pp.asp?c=gtIUK4OSG&b=126332
They do AMAZING work with animals, and their animal hospital is open 24/7 for emergency and critical care, treating the whole spectrum of different animals. They do everything at this hospital from caring for animals in crises to cardiology to dermatology to oncology... basically, anything with an "ology" on it, lol. They've been taking great care of Frodo since he broke his leg, and the vets are great - they call me back and check-in with me to make sure he's doing well. And as an added bonus, they always remember Frodo - he's a big hit over there
Just thought I'd share a great resource for folks in the area and for a cause to donate to!!