wow that can be really hard .. there are so many valueable cahrities, that choosing one per week may be too little :D just by browsing the comments ... nevertheless i want to introduce you to sadhana forest
they work for the motto

"give a poor person food, and he´ll have something to eat for one day. give him a tree, and he´s fed for life"

this is their homepage http://sadhanaforest.org/
you can contact them there ... they have forests in india, kenya, haiti
their latest project is kenya, and it´s huge
https://www.globalgiving.org/projects/long-term-food-security-for-samburus-in-kenya/?rf=ggWidget

i know the founder in person, his name is Aviram .. he´s commited to sadhana forest with all his heart since 10 years now...
I state that I´ll donate all rewards of my comment in case sadhana forest wins.