FREE offers for tools specifically for the Hack4Change participants from Intel, Socrata, Flowdock, and AgileZen.  Go to  the page for tools on hackpad for the links so you can get the free offers for them.

Tools

Open Source Accessibility Toolkit (OSAT) - "An open source approach to measuring transportation accessibility"
Crunches geodata into gorgeous 3D KML polygon representations that can be overlaid on Google Earth. It allows you to map data to both "heat" as well as "height" which makes it easy to identify interesting correlations (I.E. something that was green, but tall, might suggest an anomaly)

Ushahidi / CrowdMap - "free and open source software for information collection, visualization and interactive mapping."
Tools to empower citizens to report and aggregate and correlate information from their community. Used by the 2012 Obama campaign.

Bootstrap - "Sleek, intuitive, and powerful front-end framework for faster and easier web development."
A powerful tool for quickly spinning up new websites. Does a lot of the dirty work. Nice platform for trying out new app ideas in a hackathon setting.

Socrata Community Data Platform -- available for free to any community group organizing a hackathon  (one of the organizers just needs to register for it).  Includes a free instance of the full Socrata open data platform (which is what Data.Seattle.Gov uses, for example), hosted for free (and with no expiration), and the Socrata API tools and support.

APIhub.com - database of APIs (some open, some not)

Foursquare API --Useful API with a database of places

hackpad set up for Hack for Change - collaborative tool for sharing, editing, and organizing ideas & documents for the Hack for Change.  Create, edit, and/or Follow 'hackpads' that are set up for specific topics/groups/challenges.  Use it to share questions, ideas, answers; introduce yourself & connect with others that are in the same group or working on the same things.

Data

Open Data Government Sites (Data.gov)  - a list of government agencies that have open data

Insipration

Open City - Civic apps built with open data.  A group in Chicago that creates apps with open data to help citizens understand their government, and to make government more transparent..  Their apps are open source (MIT License); could be good for inspiration.

Guidelines and Help (documentation)

"Civic Hackathon Challenge Design Principles::  Making Data Relevant and Useful for Individuals and Communities" (pdf document)  Guidelines and ideas from folks at Intel Labs so that folks can  take big data  and vague questions and come up with solutions that will be truly useful to those that need them.