Tech Soup
www.techsoup.com
Gain access to donated and discounted technology for nonprofits.  Save hundreds of dollars on everything from Microsoft Office to Adobe software.

Open Office
www.openoffice.org
Download a free, complete suite of office software, including a word pressessor (like Microsoft Word), a spreadsheet (like Excel), a presentation software (like PowerPoint), and others.

Google Docs
www.docs.google.com
Sign up for a free google account and get access to a web-based suite of office software.  Nothing to download, and all the files are automatically saved online.  Share and collaborate live on the same file with multiple people.

Donor & Membership Management

These databases are critical to keep track of your donors, members, and other constituents to your organization. Send communication to targeted groups of people, keep track of donations, note who showed up to what event, etc.  These tools are important for anyone running a grassroots organizing or fundraising campaign.

While the "industry standard" software costs thousands, there are some free alternatives that do a great job. 

Civi CRM
www.civicrm.org
A free, open source software to keep track of your contacts, meetings, donations, and more.  Built specifically for nonprofits and grassroots organizations.  May take some expertise to customize it for your needs, but there are many conslutants and businesses that can help you.