Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski
A nice and simple gray stucco material. Great on its own, or as a base for a new pattern.
Source Bartosz Kaszubowski
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
A floral background formed from numerous clones of flower 117.
Source Firkin
The image depicts a seamless pattern of a Japanese family crest called "chidori" in Japanese .A chidori in Japanese means a plover in English.
Source Yamachem
There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Sharp pixel pattern, just like the good old days.
Source Paridhi
A seamless pattern from a tile drawn in Paint.net and vectorised in Vector Magic
Source Firkin
This is so subtle you need to bring your magnifier!
Source Carlos Valdez
Classy golf-pants pattern, or crossed stripes if you will.
Source Will Monson
A seamless pattern the unit cell for which can be had by selecting the rectangle in Inkscape and using shift+alt+i
Source Firkin
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
A pattern formed from a squared tile. The tile can be accessed in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Might not be super subtle, but quite original in its form.
Source Alex Smith
A dark metallic background with a pattern of stamped dots. Here's a dark "metallic" background pattern for you.
Source V. Hartikainen