Brushking is one of the great freebie sites flying around on the interweb that offers some amazing brushes for free! Most, if not all of them are available for use under the open-source license, although common decency dictates that you give notice to the creator of the brush first before using them. As a personal rule, whenever I download freebie stuff that I may find useful in the immediate future, I always try to get intouch with whoever created it and state my possible intentions. If you give credits to whom it belongs and you might get extra brownie points lol!
Although I havent had the oppurtunity to use the numerous amounts of brushes you can get from them on a live project, it is a pretty handy site to have in your bookmark, if not for source of free photoshop brushes then as a reference in case you might want to create your own custom-made photoshop brush.
here is the link: www.brushking.eu
I will be putting more fantastic and useful web source links here in the future so stay tuned!!