Geometric triangles seem to be quite hot these days.
Source Pixeden
The tile for this is based on a repeating unit close to a design on Pixabay. It can be had by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Background formed from the iconic plastic construction bricks that gave me endless hours of fun when I was a lad.
Source Firkin
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
This is the remix of "blue wave-seigaiha".The image depicts a seamless pattern of the front upper part of Japanese five yen coin which is used currently.This design represents a rice with ripe golden ears.
Source Yamachem
Derived from a corner decoration itself found as a jpg on Pixabay.
Source Firkin
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Prismatic Abstract Background Design No Black
Source GDJ
Geometric triangles seem to be quite hot these days.
Source Pixeden
Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.
Source Firkin
A free web background image with a seamless concrete-like texture and an Indian-red color.
Source V. Hartikainen
Made by distorting a simple pattern using the 'sin waves' plugin for Paint.net and vectorising in Vector Magic
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
Clean and crisp lines all over the place. Wrap it up with this one.
Source Dax Kieran
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Zero CC tileable yellow craft paper; scanned and made by me. CC0
Source Sojan Janso
Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
This background pattern has futuristic look. So, maybe it could be used on websites or blogs dedicated to video games?!
Source V. Hartikainen
Some rectangles, a bit of dust and grunge, plus a hint of concrete.
Source Atle Mo