A good starting point for a cardboard pattern. This would work well in a variety of colors.
Source Atle Mo
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i
Source Firkin
This one is amazing, truly original. Go use it!
Source Viahorizon
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
Abstract Ellipses Background Grayscale
Source GDJ
Can never have too many knitting patterns, especially as nice as this.
Source Victoria Spahn
A huge one at 800x600px. Made from a photo I took going home after work.
Source Atle Mo
emixed from a JPG that was uploaded to Pixabay by Kyotime
Source Firkin
This light background pattern has a texture of "frozen" surface with diagonal stripes. Here's an yet another addition to the collection of free website backgrounds.
Source V. Hartikainen
Number 1 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
An abstract web texture of a polished blue stone (or does it look more like ice).
Source V. Hartikainen
Tweed is back in style – you heard it here first. Also, the @2X version here is great!
Source Simon Leo
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
Farmer could be some sort of fabric pattern, with a hint of green.
Source Fabian Schultz
A textured orange background pattern with vertical stripes.
Source V. Hartikainen
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
Dark, crisp and subtle. Tiny black lines on top of some noise.
Source Wilmotte Bastien
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
A pattern drawn in Paint.net and vectorized in Inkscape.
Source Firkin
Zero CC asphalt, pavement, texture, photographed and made by me. CC0 WARNING I FOUND A SEAM ON THIS TEXTURE
Source Sojan Janso
From a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
Prismatic Groovy Concentric Background 2 No Black
Source GDJ
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin