Using textures mostly helps creating surprising designs (both in good & bad ways). But it is certain that, quality textures, when used wisely, will end up nicely.
ZenTextures is an online gallery presenting beautiful free textures.

Textures are very well-categorized like: paper, grunge, wood, stone & more.
Currently, there are 400+ textures shared which are free to use for both personal & commercial projects.
SeamlessTextures.net is a website presenting 55+ free textures & more added frequently.
From paper textures to grunge textures, all images are well-categorized.

The website is focused on seamless textures: textures that can be repeated infinitly without showing any edges.
They are created from creative commons licensed images that can be found on the net. And, you can also reach the source images of every texture presented.
ava7 patterns, a website with a beautiful interface, is presenting 980+ free patterns.
Patterns are very well categorized as it is possible to sort them with colors & shapes.

With a click, they can be previewed live at the ava7 patterns website.
It is also possible to comment & rate them as well as sorting them with:
- top rated
- most commented
- most downloads
BgPatterns is a pattern library where you can find, create & share patterns.
You can create the patterns from ready-to-use images by changing the colors & canvas and scaling or rotating them. And this process is done with a slick interface.

The pattern design interface lets you preview them easily.
And, you can also check the recently created and popular patterns.
Everyday Icons has a playground area, which has a chic interface, presenting free patterns, icons & some PDF note designs.
Specially, patterns are high quality, can be previewed & downloaded in different colors.
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Currently, you can find 100 patterns and 6 small icon sets.
DinPattern by Evan Eckard is a website presenting quality & unique patterns created by him.
Currently there are 60+ free patterns to use.

New patterns are being added by time and before downloading them, you can easily preview how they look.
Backgrounds, patterns can easily change the total look & feel of a website.
Squidfingers is sharing 150+ patterns that can be used in our designs.

Click to check them out.
Free grunge textures can be found at Grungetextures.com, a website which collects and presents great free grunge textures.
Textures are high quality JPG files and licenced as free for personal and non-profit use.

Textures are categorized well for easier navigation. For ex: you can easily find the wood textures, stone textures or the other ones.