Know of any new ones or any we missed? Post them in the comments!
#International
Consider signing the Women's Human Rights Campaign's Declaration on Women's Sex-Based Rights and getting connected with other feminists through their website. They are helping women to organize all over the world.
#British Isles
ReSisters United - UK and Ireland
Lleisiau Merched Cymru (Women's Voices Wales) - Wales [Facebook Link]
#Canada
Canadian Women's Sex-Based Rights aka caWsbar - National
#New Zealand
#United States
Feminists in Struggle - National