From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from a drawing in 'The March of Loyalty', Letitia MacClintock, 1884.
Source Firkin
Prismatic Abstract Geometric Background 2 No Black
Source GDJ
The image is a seamless pattern of a fishnet.
Source Yamachem
You may use it as is, or modify it as you like.
Source V. Hartikainen
Super subtle indeed, a medium gray pattern with tiny dots in a grid.
Source Designova
This is the remix of an Openclipart clipart called "Maze" uploaded by "any_ono_mous".Thanks.This is a seamless pattern of a maze.
Source Yamachem
Floral patterns might not be the hottest thing right now, but you never know when you need it!
Source Lauren
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Adapted heavily from a JPG that was uploaded to Pixabay by Viscious-Speed.
Source Firkin
Black brick wall pattern. Brick your site up!
Source Alex Parker
This ladies and gentlemen, is texturetastic! Love it.
Source Adam Pickering
This seamless background image should look nice on websites. It has a dark blue gray texture with vertical stripes, it tiles seamlessly and, like all of the background images here, it's free. So, if you like it, take it!
Source V. Hartikainen
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Three shades of gray makes this pattern look like a small carbon fiber surface. Great readability even for small fonts.
Source Atle Mo
A seamless pattern formed from cross 4. To get the original tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Derived from an image that was uploaded to Pixabay by starchim01
Source Firkin
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868
Source Firkin
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim