This is a collection of QGIS symbols and styles.
Please use this download link to download the collection: https://github.com/anitagraser/QGIS-resources/zipball/master
Of course you can also use Git. This way, you can easily update to the latest versions of all styles.
Feel free to send pull requests if you want to add to this collection. Until the QGIS project gets dedicated infrastructure for sharing symbols and styles, I think this could be a good way to go.