Elementary icons are elegant and created by Magog64. Elementary icons offers more than 13,000 icons for Linux. This icon set can fit with any kind of light and dark theme but according to creator these icons are specially optimized for Elementaryish dark-panel theme. Also check icons collection
You can use Unity Tweak ToolGnome-tweak-tool or Ubuntu-Tweak to change icons.
elementary icons

elementary icons

elementary icons

elementary icons

To install MyElementary icons in Ubuntu 14.10/14.04/12.04/Linux Mint 17.1/17/13 open Terminal (Press Ctrl+Alt+T) and copy the following commands in the Terminal:
That's it
Source: My-Elementary
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