A collection of online activist handbooks, tips and tricks from a diverse array of sources:
Protest.net offers this reprint of articles from Activism 101 and the Freedom Writer on their website.
The Midnight Law Collective has assembled these materials related to staying safe, even in large demonstrations. They also offer trainings on legal support for small actions as well as for non-violent direct action.
Jim Britell's "Organize to Win: A Grassroots Activist's Handbook"
(A Guide to Help People Organize Community Campaigns)
"Activist's Grass Roots Handbook"
compiled by William H. Dailey, Esq.
"Managing the Media: A Guide for Activists"
by Carol Fennelly
Bastard Nation's "Tips for Tabling"