Dark Brick Pattern #1032
Stone CC BY-SA 3.0A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
More Textures
Noise Lines@2X #898
Paper CC BY-SA 3.0Lovely pattern with some good-looking non-random noise lines.
Source Zucx
Background pattern 254 #2144
Dark CC 0To get the tile this is based on select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Tessellation 15 (colour 4) #2219
Green CC 0The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
Background pattern green #2027
Green CC 0Remixed from a design seen in 'Burghley. The Life of William Cecil', William Charlton, 1857. The tile this is based on can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Floral pattern 11 #1770
Dark CC 0From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Abstract Ellipses Background Grayscale #814
Dark CC 0Abstract Ellipses Background Grayscale
Source GDJ
Background Patterns - Cerulean #245
Fabric CC 0f you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Batthern #324
Grid CC BY-SA 3.0Sometimes simple really is what you need, and this could fit you well.
Source Factorio.us Collective
Prismatic Abstract Line Art Pattern Background 2@2X #568
Dark CC 0Prismatic Abstract Line Art Pattern Background 2
Source GDJ
Background pattern 271 #2058
Dark CC 0Remixed from a drawing in 'The Canadian horticulturist', 1892
Source Firkin
Rough Concrete Surface #1195
Concrete CC BY-SA 3.0This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
Leafy pattern 9 #1802
Green CC 0Remixed from an image that was uploaded to Pixabay by KirstenStar
Source Firkin
Prismatic Abstract Geometric Background 5 No Black #402
Noise CC 0Prismatic Abstract Geometric Background 5 No Black
Source GDJ
Whitey@2X #110
Light CC BY-SA 3.0A white version of the very popular linen pattern.
Source Ant Ekşiler
Dark Denim@2X #373
Dark CC BY-SA 3.0Thin lines, noise and texture creates this crisp dark denim pattern.
Source Marco Slooten
Decorative divider 282 #1857
Dark CC 0From a drawing in 'In an Enchanted Island', William Mallock, 1892.
Source Firkin