The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Not the most creative name, but it’s a good all-purpose light background.
Source Dmitry
Zero CC tileable cork floor, photographed and made by me. CC0
Source Sojan Janso
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
Remixed from a drawing in 'Sun Pictures of the Norfolk Broads', Ernest Suffling, 1892.
Source Firkin
A seamless marble-like texture colored in light blue.
Source V. Hartikainen
An abstract Background pattern of purple twisty patterns.
Source TikiGiki
A seamless pattern formed from a tile made from ornament 22. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A tile-able background for websites with paper-like texture and a grid pattern layered on top of it.
Source V. Hartikainen
A grayscale fabric pattern with vertical lines of stitch holes.
Source V. Hartikainen
A seamless paper background texture colored in pale yellow. This seamless texture is ideal for those who need a yellow background image for their website. The texture resembles paper.
Source V. Hartikainen
A free seamless background image with a texture of dark red "canvas". It should look very nice on web sites.
Source V. Hartikainen
Number 2 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
Adapted from an image that was uploaded to Pixabay by Anerma.
Source Firkin
You may use it as is, or modify it as you like.
Source V. Hartikainen
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
This is indeed a bit strange, but here’s to the crazy ones!
Source Christopher Buecheler
Same as gray sand but lighter. A sandy pattern with small light dots, and some angled strokes.
Source Atle Mo
A seamless texture of black leather. I think it will look best when used in headers, footers or sidebars.
Source V. Hartikainen
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward