I am a self-taught data geek who has mostly worked in the U.S. Labor Movement.
I was first inspired by some amazing union organizers in New Orleans. They showed me how the Union was an institution that could mobilize serious change for poor working people, especially women of color. I made myself useful by creating a simple database to help keep track of all the names and phone numbers and other notes scattered on post-it notes by their organizers.
Today, I live in China and continue to dedicate myself to supporting progressive organizers -- introducing new technology for smarter outreach and mobilization.
Rini Art is the best collection of images for activists. They are free and designed by a passionate artist and activist. You'll find great images that are bold and emotional. Images of people doing things like demonstrating with banners, marching in the streets, and holding picket signs.
Best of all they are free to use.
Because they are originally block prints, they are really excellent for producing in black and white. They can be scaled up or down. As the site itself notes, the higher quality images are downloadable in Bitmap TIFF format. Use the GIF format for lighter-weight use online or smaller documents.
The New Organizing Institute's toolbox is an amazing collection of training materials -- videos, powerpoints, and other documents. And it's free.
They bring together very practical tools for building a team and putting ideas into action. Some of the most helpful concepts are the Story of Self and the Theory of Change. Additionally, they offer some great resources on the techie components of launching an issue or political campaign. I especially love all their great training materials on data management.