If you are planning to make (nice looking) maps, you might want to check out QGIS. It amongst others offers a lot of options and flexibility to make your own symbols (see e.g., this blog for a nice example).
But not everybody will want to develop their own sets of symbols, so having a nice set of symbols to choose from would definitely be an asset.
And this is exactly what Mithantrope’ s Thoughts is providing. Check out his blog post QGIS symbology set, which provides a whole set of great looking QGIS symbology. And if you like it, you can download it and start using it (instructions are included).