Background pattern 6 #225
Noise CC 0Another fairly simple design drawn in Paint.net and vectorized in Inkscape.
Source Firkin
More Textures
Wood Pattern #370
Wood CC BY-SA 3.0One of the few full-color patterns here, but this one was just too good to pass up.
Source Alexey Usoltsev
Batthern #324
Grid CC BY-SA 3.0Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Background pattern 252 #2162
Dark CC 0Recreated 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
overlay crack #153
Noise CC 0This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
Decorative divider 284 #1848
Dark CC 0From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin
Tileable Wood@2X #656
Wood CC BY-SA 3.0Not so subtle. These tileable wood patterns are very useful.
Source Elemis
Robots #125
Dark CC BY-SA 3.0And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
blue glass design #2545
Blue CC 0The image is a design of blue glass.How about using it as background image?
Source Yamachem
Diamond pattern (colour 6) #2280
Yellow CC 0From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Decorative divider 211 #2362
Dark CC 0From a drawing in 'Storia del Palazzo Vecchio in Firenze', Aurelio Gotti, 1889.
Source Firkin
Circular frame 26 #1711
Dark CC 0Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
Orange-red Pattern #995
Stripes CC BY-SA 3.0Orange-red pattern for tiled backgrounds.
Source V. Hartikainen
Subtle White Feathers #1103
Light CC BY-SA 3.0This one is amazing, truly original. Go use it!
Source Viahorizon
Grid #974
Gray CC BY-SA 3.0There are quite a few grid patterns, but this one is a super tiny grid with some dust for good measure.
Source Dominik Kiss
Decorative divider 288 #1820
Dark CC 0From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin