Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
The first pattern on here using opacity. Try it on a site with a colored background, or even using mixed colors.
Source Nathan Spady
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Nice and simple crossed lines in dark gray tones.
Source Stefan Aleksić
Different from the original in being a simple tile stored as a pattern definition, rather than numerous repeated objects. Hence easy and quick to give this pattern to objects of different shapes. To get the tile in Inkscape, select the rectangle and use shift+alt+i.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
Remixed from a drawing in 'A Girl in Ten Thousand', Elizabeth Meade, 1896.
Source Firkin
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman
Prismatic Polka Dots Mark II No Background
Source GDJ
Here's a brown background pattern with subtle stripes. I hope you'll like the color. If not, feel free to change it using an image editor, if you know how of course. Personally, I'm using GIMP to create these backgrounds.
Source V. Hartikainen
A bit like some carbon, or knitted netting if you will.
Source Anna Litvinuk
A seamless pattern the starting point for which was a 'rainbow twist' texture in Paint.net.
Source Firkin
Feel free to use this seamless background texture as a background on a web site. It's colored in a light pink color and is seamlessly tile-able.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz
Prismatic Polka Dots 3 No Background
Source GDJ
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
More in the paper realm, this time with fibers.
Source Jorge Fuentes
Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Derived from an image that was uploaded to Pixabay by pugmom40
Source Firkin
I’m starting to think I have a concrete wall fetish.
Source Atle Mo