With subtlepatterns.com you can simply browse all of the backgrounds and when you find one that you like you can download the image. He even provides a 2x version for use with high density displays. If you are willing, you can even purchase his PhotoShop extension here for $11.99. It will automatically sync the images and will help streamline your design workflow.
Subtlepatterns.com is a great free resource for high quality repeating backgrounds for use in your designs. It was created and is actively maintained by Atle Mo.