The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A seamless textured paper for backgrounds. Colored in pale orange hues.
Source V. Hartikainen
From a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
A seamless background pattern of dark brown wood planks.
Source V. Hartikainen
Hexagonal dark 3D pattern. What more can you ask for?
Source Norbert Levajsics
A blue background wallpaper for websites. It has a seamless texture with vertical stripes. It looks quite nice not only when using as a tiled background on websites, but also on computer desktops.
Source V. Hartikainen
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
Seamless pattern formed from a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Submitted by DomainsInfo – wtf, right? But hey, a free pattern.
Source DomainsInfo
Subtle scratches on a light gray background.
Source Andrey Ovcharov
Remixed from a drawing in 'Jezebel's Daughter', Wilkie Collins 1880
Source Firkin
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
The name tells you it has curves. Oh yes, it does!
Source Peter Chon
The tile this is formed from can be retrieved in Inkscape by selecting the rectangle and using shift+alt+i
Source Firkin
Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.
Source Atle Mo
This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
It almost looks a bit blurry, but then again, so are fishes.
Source Petr Šulc
A simple but elegant classic. Every collection needs one of these.
Source Christopher Burton
A version without colours blended together to give a different look.
Source Firkin