There are websites like http://alfredworkflow.com and Packal which have hundreds of available workflows which you can download for free.
There is Workflow Searcher Alfred Workflow which lets you find and install alfred workflows available on http://www.alfredworkflow.com/ from within Alfred itself. which you can download from here
There is also awm (Alfred Workflow Manager) which lets you find and install workflow found on Packal using the terminal. It requires you to have node and the node package manager npm installed.