A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
A textured blue background pattern with vertical stripes.
Source V. Hartikainen
Bright gray tones with a hint of some metal surface.
Source Hendrik Lammers
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
A seamless pattern formed from background pattern 102
Source Firkin
Dark wooden pattern, given the subtle treatment. based on texture from Cloaks. https://cloaks.deviantart.com
Source Atle Mo
A seamless pattern formed from a tile made from page ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Remixed from a drawing in 'Chambéry à la fin du XIVe siècle', Timoleon Chapperon, 1863.
Source Firkin
Prismatic Hexagonalist Pattern No Background
Source GDJ
Crossing lines with a subtle emboss effect on a dark background.
Source Stefan Aleksić
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
One more from Badhon, sharp horizontal lines making an embossed paper feeling.
Source Badhon Ebrahim
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by pugmom40
Source Firkin
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
One more in the line of patterns inspired by Japanese/Asian styles. Smooth.
Source Kim Ruddock
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Could remind you a bit of those squares in Super Mario Bros, yeh?
Source Jeff Wall
I’m not going to lie – if you submit something with the words Norwegian and Rose in it, it’s likely I’ll publish it.
Source Fredrik Scheide
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless background drawn in Paint.net and vectorised with Vector Magic. The starting point was a photograph of drinking straws from Pixabay.
Source Firkin
From a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
Colourful background achieved with gradient fills.
Source Firkin