Unsplash.com: the best collection of high-quality, free, copyright friendly photos on the Web
Freepik: free photos, vector graphics, and other good stuff
GraphicBurger: lots of free design resources, including icons, vector graphics, and templates
Freesound: all kinds of music as well as ambient sounds
Pixlr: a free online image editing program; useful if you have to resize or crop images; Pixlr X is super easy, Pixlr Editor has more options and requires a Flash download
