There are dozens to techniques you can use to create you own seamless textures and patterns. Here are few to get you started:
How to Turn a Texture into a Seamlessly Tiled Background - In this quick tutorial from PSD Tuts+ you'll learn how to take a texture and turn it into a background image ready for seamless tiling.
Photoshop Video Tutorial - Seamless Texture Creation - How to turn an image into a seamless pattern. Can be done with photos and also your own texture work--very helpful for 3D work, Second Life, website backgrounds, etc.
How To Create Repeating Texture & Pattern Images - Repeating background images are safest method of styling up your website. Let's take a look at how seamless or repeating textures and patterns can be created in Photoshop.
There are a number of programs available to assist with the creation of seamless patterns, textures and backgrounds:
Seamless Texture Generator - a tool for creating professional seamlessly-tileable textures from photographs quickly and easily.
Genetica - Powerful node-based texture generator for making tiling or seamless textures for games or other 3D work.
Filter Forge - A visual node-based editor allowing you to create your own filters, textures, effects, distortions, backgrounds, frames, you name it. All filters automatically support 16- and 32-bit modes in Photoshop, real-world HDRI lighting, bump and normal maps, huge resolutions, and most filters can be seamlessly tiled.
Pattern Studio - Pattern Studio is a special editor for creating seamless textures and patterns. Such textures can be used for 3D applications, cloth design, scrap-booking, web etc.
Texture Maker - Texture Maker is a seamless texture generator and designer. The application contains everything needed to create seamless textures for use in 3D rendering packages, game development, web graphics, image and video editing.
Here are some free image archives where you can find source images for texture creation:
Pixel Perfect Digital - Free Stock Photos, Backgrounds and Textures with Creative Commons Attribution Licensing
Grunge Textures - We provide quality background textures to photographers, artists and other creative professionals. We specialize in weathered and worn surfaces. Small versions of our textures may be used free of charge.
Design Packs - High quality image collections that can be use in both personal and commercial web design projects. Each collection features a group of 15 images that share a common theme. We've created dozens of collections based on a variety of themes.
Stockvault - Free Photos and Free Images for personal, educational and non-commercial usage.
MorgueFile - Free images for your inspiration, reference and use in your creative work, be it commercial or not!
ImageAfter - Image*After is a large online free photo collection. You can download and use any image or texture from our site and use it in your own work, either personal or commercial.
OpenPhoto - OpenPhoto is a high-quality photo sharing platform created in 1998. OpenPhoto contributors offer their images for free under terms of Creative Commons licensing.
Texture King - Free high resolution, high quality textures for personal and commercial use.
Urban Dirty - Urban Dirty is a regularly updated online photo library featuring 800 gritty, grimy and sometimes slimy images for use in design and artwork creation.
Lost and Taken - A design blog that focuses on giving away free, high-resolution textures.
Browse our collection of Free Seamless Textures, Background and Patterns.