As of today I use openclipart.org as the main source of all resources (images) for my apps. I have learned this the hard way … after having a short but interesting relation with oDesk.
It started with my Memo game. I was looking for 20 cartoon style images of different animals. I learned about oDesk from a friend and quickly registered and posted an offer “20 images for a kids game required”. In a mater of minutes first reply was posted and after 2-3 days I had few to choose from. My mistake – I have choosen the cheapest one, that guy from Pakistan had a good portfolio so I thought I am on my way to get pretty images cheap. I described what I looked for and in 2 days I had beautifull images in my inbox. Luckilly for me I had a short market research via images.google.com and I linked the nice images with the similar ones I have seen somewhere. After 15 mins of playing with images.google.com I found them … my graphic expert from oDesk took a copyrighted images, recolored them and tried to sell.
On that day I lost all trust I had in cheap workforce you can hire in low cost locations overseas. Sorry folks, no more offers from me. I found http://openclipart.org and I use it for all my needs – with thousands of images there – all public domain it is a matter of time to collect the images you need.
After my experience with images I have not even posted an offer for music or sound effects – instead I googled for open alternatives and found http://ccmixter.org/ – its not as easy in use as openclipart (checking an image takes blink of an eye, checking a mp3 clip takes minutes) but its good starting point. Just remember that CC license expects you inform audience who is the author of the music clip, and not all varietes of CC allow commercial usage or modifications.
If you have any similar repositories of public domain or creative commons licensed content please use comments to let others know.