Classic 45-degree pattern, light version.
Source Luke McDonald
Derived from elements found in a floral ornament drawing on Pixabay.
Source Firkin
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
A comeback for you: the popular Escheresque, now in black.
Source Patten
Sharp pixel pattern, just like the good old days.
Source Paridhi
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
From a drawing in 'An Old Maid's Love. A Dutch tale told in English', Maarten Maartens, 1891.
Source Firkin
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
This texture looks like old leather. It should look great as a background on web pages.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Kaz
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Prismatic Floral Pattern 3 Variation 3 No Background
Source GDJ
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Gold Triangular Seamless Pattern No Background
Source GDJ
Remixed from a drawing that was uploaded to Pixabay by DavidZydd
Source Firkin
Derived from an image that was uploaded to Pixabay by TheDigitalArtist
Source Firkin
The image depicts a seamless pattern of Japanese Edo pattern called "kikkou-matsu" or "亀甲松" meaning " tortoiseshell-pinetree".The real pinetree is like this: https://jp.pinterest.com/pin/500744052301065077/
Source Yamachem
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Alternative colour scheme for the original floral pattern.
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
There are many carbon patterns, but this one is tiny.
Source Designova
Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective