The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
A series of 5 patterns. That’s what the P stands for, if you didn’t guess it.
Source Dima Shiper
Prismatic Geometric Tessellation Pattern No Background
Source GDJ
The classic subtle pattern. Sort of wall/brick looking. Or moon-looking?
Source Joel Klein
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
This is one good-looking pattern. Grab it!
Source Omur Uluask
A seamless pattern formed from a rectangular tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Heavy depth and shadows here, but might work well on some mobile apps.
Source Damian Rivas
A seamless gray background texture suitable for use on websites. To me, it has the look of stone. Feel free to modify it to meet your needs (by making it a bit lighter or darker, for example).
Source V. Hartikainen
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
So tiny, just 7 by 7 pixels – but still so sexy. Ah yes.
Source Dmitriy Prodchenko
A hint of orange color, and some crossed and embossed lines.
Source Adam Anlauf
The rectangular tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Derived from a design in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
You don’t see many mid-tone patterns here, but this one is nice.
Source Joel Klein
Colour version of the original pattern inspired by the front cover of 'Old and New Paris', Henry Edwards, 1894.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Prismatic Abstract Geometric Background 5
Source GDJ
A seamless pattern formed from cross 4. To get the original tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin