http://psd.tutsplus.com/tutorials/designing-tutorials/how-to-create-long-shadow-effects/

Part of the recent, “flat design” trend, long shadow effects are a popular but not necessarily new phenomenon. The trend’s strongest impact seems to be on interface design elements and icons but it is being increasingly used as part of web designs, as well. In this tutorial, we will show you 4 ways that you can create long shadow effects in Photoshop using several different tools. Let’s take a look!