D3

Official D3 Site
Official D3 Wiki
D3 API Reference
D3 Tutorial by Scott Murray (highly recommended! - Required D3 textbook is based on this.)
D3 on Stack Overflow
D3.js Google Group
Mike Bostock’s site
D3.js Gallery
Mike Bostock on bl.ocks.org
Jérôme Cukier and Scott Murray’s D3 tutorial at the Strata Conference
D3 For Mere Mortals
Mike Bostock’s D3 Tutorial
Vadim’s Lecture Slides, D3
Jerome Cukier’s D3 Cheat Sheet
FlowingData D3 Tips
D3, Conceptually
D3 Tutorial Videos by Ian Johnson - Vol I
D3 Tutorial Videos by Ian Johnson - Vol II
D3 Tips and Tricks
TopoJson
D3 Gallery

Web Development

Enabling Web Developer Extensions in the Browser
Eloquent Javascript Book
Mozilla Developer Network
DevDocs - Unified documentation on all web technologies
Dive Into HTML5 - Homepage
Dive Into HTML5 - Canvas

Git

Official git command line and GUI clients, official documentation

Clients

GitHub Client for Mac
GitHub Client for Windows
SourceTree for Mac and Windows
TortoiseGit for Windows

Tutorials etc.

Setting up git
Understanding git conceptually

Data Sources

Wolfram Alpha
Quandl
Datamob
Factual
Metro Boston Data Common
Census.gov
Data.gov
Dataverse Network
Infochimps
Linked Data
Guardian DataBlog
Data Market
Reddit Open Data
Climate Data Sources
Climate Station Records
CDC Data
World Bank Catalog
Free SVG Maps
UK Office for National Statistics
StateMaster

Web Sites & Blogs

eagereyes
Gapminder
Flowing Data
Perceptual Edge
Information Aesthetics
Visual Complexity

Exploratory Data Analysis

These tools help you to get an idea about the shape and properties of datasets and let you produce good (standard) plots.

Tableau

Online Help
Quick Start Guides
Knowledge Base
Training and Tutorials
Tableau Public Gallery

Others

Plot.ly
Wolfram Mathematica
Many Eyes

Python

Python is great for data analysis and for data scraping.

Python
Enthought Python Distribution
The Python Tutorial
Learn Python the Hard Way
Google’s Python Class
IPython
The Python Package Index
SciPy
NumPy
Matplotlib

Pattern - a data scraping library
Beautiful Soup - the “mother” scraping library

Other Software Toolkits

Plot.ly
Wolfram Mathematica
Harvard-specific Installation Guidelines
Protovis (JavaScript)
Prefuse (Java)
Flare (ActionScript)
Piccolo (Java / C#)
Microsoft Vedea
25 Tools
75+ Tools

Processing

Processing main page
Learning Processing
OpenProcessing.org
Examples by Ben Fry
Using Processing in Eclipse