One of the biggest challenges for me is often where to get good graphics and sound resources. There are already a lot of lists from other developers available, but still my own list might be useful for you, too. 🙂
Disclaimer: Of course, please always check the license terms of the different sites, if it fits to what you want to use the resources for. Also, please note that my comments to the licenses are no legal advice and might be outdated at the time you read this.
In general, if I am in doubt if I am allowed to use something for my purposes, I had good experiences with contacting the authors directly and ask for permissions. Often people are happy to be asked and allow usage of their work even for commercial use.
- stock.xchng: Really a lot of high quality photos, free to use for a lot of purposes, but with unclear license terms for commercial reuse.
- morgueFile: A lot of photos, not of that high quality as at stock.xchng, but with explicit allowance to use the photos also for commercial purposes.
- Flickr: Great photos and a lot of users allow reuse of their photos, but you have to check the license of the photos separately.
- Wikimedia Commons: A repository of free images, sound and other multimedia files. You can find good photos there, but always check the license of the individual photo before using it.
- Google Image Search: If you go to the advanced search options, there is option to only show images with the license you need.
- Icon Finder: A searchable directory of lots of high quality icon sets often available for commercial reuse
- iconPot: Lists free icon sets sorted by categories
- A lot of free icons are available at iconsweets and iconsweets2
- A big free icon set is available at glyphish.com
- CGTextures: A huge categorized collection of high quality textures free to use in commercial projects
- OpenClipArt: A huge collection of clip art of all kind free to use for all purposes