Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
Not a pattern for fabrics, but one produced from a jpg of a stack of fabric items that was posted on Pixabay. The tile that this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Pattern formed from simple shapes. Black version.
Source Firkin
ZeroCC tileable beechwood wood texture, generated in Neo Texture Edit by me. CC0
Source Sojan Janso
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This is the third pattern called Dark Denim, but hey, we all love them!
Source Brandon Jacoby
Number five from the same submitter, makes my job easy.
Source Dima Shiper
This was formed by distorting an image of a background on Pixabay.
Source Firkin
Vector version of a png that was uploaded to Pixabay by pencilparker
Source Firkin
Super dark, crisp and detailed. And a Kill Bill reference.
Source Badhon Ebrahim
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Zero CC tileable ground (#2) cracked, crackled texture, made by me. CC0
Source Sojan Janso
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
Bigger is better, right? So here you have some large carbon fiber.
Source Factorio.us Collective
This beige background pattern resembles a concrete wall with engravings or something similar to it.
Source V. Hartikainen
Seamless pattern inspired by a drawing on Pixabay. To get the tile this is formed from, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Floral patterns might not be the hottest thing right now, but you never know when you need it!
Source Lauren
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
A set of paper filters. The base texture is generated the same way, only the compositing mode is varied.
Source Lazur URH
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A pattern formed from a photograph of a 16th century ceramic tile.
Source Firkin
An attempt for cleaning up the original image in a few steps.
Source Lazur URH