Giving time, effort and energy is something that doesn't cost money. It's not what you own or have, it's what you are and what you do that makes you who you are (Fromm articulated this well).
I went to see Peace of Heart Choir, and I thought it was really cool. They are a non-profit choir who performs at shelters, hospitals and city events in NYC. I saw them at the library. If you like to sing and have a Thursday evening free in New York City, you can join in too! They sing uplifting songs from a multicultural background. Beautiful.
New York Cares is another way to give time, effort and energy. I've only done it once, but I hope to volunteer more and more. They're doing a lot of good work in the Rockaways after Hurricane Sandy. I got a real rush out of volunteering. It's a very positive environment, and made me feel good about myself.
Of course if you want to donate energy, effort and time, Free Buddhist Audio, also needs volunteers.
And if you want to give money, I always think Karuna Trust is a great one. They work with the ex-untouchables in India who have converted to Buddhism. (They're working on a US version, so you'll have to give to the UK version at this time.)
Please feel free to add your favorite places to give from around the world in the comments!