A few months ago I installed a command line utility called hub. I'm really fond of it. It's aim is to make it easier to interact with GitHub from the commandline. It's a wrapper around the standard git command. Once it's installed you can do stuff like this (take from the manual page)

# clone your own project
$ git clone dotfiles
→ git clone git://github.com/YOUR_USER/dotfiles.git

# clone another project
$ git clone github/hub
→ git clone git://github.com/github/hub.git

# open the current project's issues page
$ git browse -- issues
→ open https://github.com/github/hub/issues
# Example workflow for contributing to a project:
$ git clone github/hub
$ cd hub
# create a topic branch
$ git checkout -b feature
  ( making changes ... )
$ git commit -m "done with feature"

# It's time to fork the repo!
$ git fork
→ (forking repo on GitHub...)
→ git remote add YOUR_USER git://github.com/YOUR_USER/hub.git

# push the changes to your new remote
$ git push YOUR_USER feature
# open a pull request for the topic branch you've just pushed
$ git pull-request

Want to use all this cool stuff too? Head over to the installation instructions on GitHub.