Learn

Here are the best resources I have come across for learning the Git distributed version control system. Feel free to open up a pull request or let me know if about any necessary fixes/updates.

Courses

O'Reilly Video - Mastering Git
PeepCode - Git Training

Videos

Terminal, Git, and GitHub for the Rest of Us: Screencast
Git, GitHub and Social Coding - By Scott Chacon, Chris Wanstrath and Tom Preston-Werner (founders of Github)
YUI Theater — Jenny Donnelly: Introduction to Git
Master Advanced Git
Simple git and github demo - NumbKnuckle (Direct video link)
Learn how to branch with git - NumbKnuckle (Direct video link)
O'Reilly Webcast: Git in one hour
Tech Talk: Linus Torvalds on git
GitCasts Screencasts
Using Git GUI with Eclipse Part I - Setting up the workspace
Using Git GUI with Eclipse Part II - Pushing changes to the server
Contributing with Git
More Git and GitHub Secrets
How GitHub Uses GitHub to Build GitHub
Jonathan Stark: An Introduction to Git

Articles

A List Apart - Get started with git
Easy version control with git
Getting the hang of GitHub
Understanding Git Conceptually
Git for Designers
Git - The Basics
Git For Windows Developers Series
Getting Started with Git on Mac OS X

Training/Tutorials

Git Immersion: Step by step tutorials
Try Git on Github: Powered by CodeSchool!
GitHub Training
Git Immersion
Git Ready
Learn Git Branching: An Interactive Git Branching Tutorial
Think Like a git

Reference

Books

Pro Git Book (free, open source, online)
Version Control with Git: Powerful Tools and Techniques for Collaborative Software Development
Pragmatic Version Control Using Git
Getting Good with git (Free ebook)

Documentation Sites

GitHub Help
Official git documentation
Gitref (also redirects from learn.github.com)
Git FAQ

GUI clients

Taken from http://git-scm.com/downloads/guis

Mac-specific

Tower: The most powerful git client for Mac
GitHub for Mac
Gitbox: The Everyday git interface for human beings.
GitX
GitX-Dev: A fork of GitX

Windows-specific

GitHub for Windows
TortoiseGit
Git Extensions

Windows and Mac

SourceTree

Windows, Linux, and Mac

Egit Eclipse plugin
SmartGit
Git Cola
Git Eye

Visual References

Git Tower's git cheat sheet
A Visual Git Reference
Git cheat sheet

Git Workflow Methodologies

The Normal Workflow
The Distributed Workflow
@Schacon: GitHub Flow
A Successful Git Branching Model
A simple git branching model
NetTuts—The Perfect Workflow: Git, GitHub, and SSH
@Wycats: Common Git Workflows

Merge vs. Rebase

@Mislav: Merge vs. Rebase
SourceTree Blog: Merge or Rebase?
Envato: Rebasing Merge Commits in Git
Only You Can Prevent Merge Commits
The Case for Git Rebase
Git Rebase Considered Awesome
@Isaacs: Git Is an Editor, and Rebase is the Backspace Key

Pull vs. Fetch

Smart Pull

Tagging

Adding and Removing Tags
GitReady: Tagging

Aliases

Git Wiki: Aliases
Everyday Git Aliases
Must-have Git Aliases
Idiot-proof Git Aliases
Streamline your workflow with git aliases

Advanced

Git Hooks
Patience Diffs
Auto Notify on Git Pull
Speed up Git 5-50x
Git rerere: teach git how to handle conflicts in the future
Git subtree: an alternative to submodules
Git bisect - Track down the commit that introduced the bug
Git reflog: your safety net
Check out GitHub Pull Requests locally
Deploying with Git
Hub
Splitting a subpath into its own repo