There are very few non-profit organizations that help animals that I find worthy of my time and money.

I, personally, stay away from the bigger groups that have plenty of money and do not always meet my expectations.  I like to give my money and time to the small groups that do some of the hardest work.  There are a few in the area but the one I am bias to is the Homeless Cat Project.  This is a non-profit organization of a few woman who, in their "spare time", help to control the over population of feral or unwanted cats.
The group started in 1998 when word got out that the Town of South Hadley was going to kill a colony of feral cats near a nursing home like facility.  The town felt like the cats were a health hazard and their solution was to kill them.  The Homeless Cat Project quickly formed and after a huge effort, persuaded the town to let the group trap the cats, spay or neuter, vaccinate and tattoo them and then put them back in the colony site.   The Homeless Cat Project used several studies done by other humane groups that showed that these colonies, if their population was controlled, would be better off  
Some of the studies showed that colonies that were killed off would be replaced with more cats, thereby, expanding the colony and not solving the problem.

The work that these woman do is amazing.  They go out in all kinds of weather into all kinds of neighborhoods to trap these cats. They then have to drive to a vet or facility with the cats to get the vet care.  Then they bring the cats back to the colony site.  They pay for their own expenses and they do not get paid at all for their time and effort.  I have been one of the vets since the group started that have provided low cost vet care for these cats.  The work is totally pro-bono but as a veterinarian, I feel driven to do what I can for all animals, even the unwanted ones.

The Homeless Cat Project is frequently struggling to find money to pay for all the vet care and most of the money comes from private donations and grants.  Please consider donating to this great organization.  Donations can be sent to:

The Homeless Cat Project
PO BOX 80256
Springfield, MA  01138-0256