Here is a great collection of hi-res sand textures for you to download; all textures that are provided by THOPPP are all subject to the following terms.
“Terms of usage” for THOPPP textures
1. Redistribution or selling any of the textures of any kind is prohibited.
2. Minor editing of textures and submitting as different resources is forbidden.
3. Don’t claim my stock as your own, don’t re-upload my stock, and don’t post art made with my stock to “photography” websites. Credit me and link back to thoppp.com or the texture pack page.
4. You may use my textures for whatever you like as long as you stick to the above rules.