Some nice textures
I ran across some seamless texture files on the following site:
http://www.renderlight.it/english/free_download.php
Mostly woods but stone and fabric as well. Not only are they perfectly seamless, but the fact that they include the bump (roughness) file is great. A gloss file is also included which can be used as an alternate bump depending on your preferences.
As always, respect the works of others and provide credit where credit is due. I have not seen any direct restrictions to using these files.
The download file format is RAR. If you do not have an UnRAR application, you can Google "unrar online" for some options.
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If you found some great free seamless texture sites, please add them in comments. Please post any restrictions you find about their use.