Seamless textures can be created fast and easy using a Tiler (extension for Photoshop).
Free 450 seamless textures
Special thanks to Agata Galewska (the author of texturify.com) for giving me the rights to make her textures seamless using my extension for Photoshop called Tiler.
Link for textures:
http://bit.ly/tiler-free
How to download textures faster (video tutorial):
https://youtu.be/ezkYMOX3RSo