Usually one of the first things I do after creating a new Git repo for a project is to put together my .gitignore file. This often involves copy/pasting from a previous project, or visiting github/gitignore.
However, thanks to gitignore.io, you can simply add a function to your command-line environment that makes it easy to quickly grab the .gitignore file you need.
For example, for an iPhone project, after initializing my repo, I can just run the following command:
gi objective-c >> .gitignore
…and a sparkly new ignore file will be created for me and is ready to use. You can find full instructions on how to use gitignore.io and set it up for command-line use at http://gitignore.io/cli.