BlendMe is a new Photoshop extension may just be one of the most useful for any type of designer. This Photoshop extension gives you free access to thousands of icons that are licensed under Creative Commons Attribution 3.0 Unported License.
You can search for icons very easily using the extension without having to leave Photoshop. Once you've found an icon you like, you can simply drag and drop it directly onto your canvas.
There are thousands of assets being added regularly and you can even add your own via their site.