A seamless pale yellow paper background with a pattern of animal tracks.
Source V. Hartikainen
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Colourful background achieved with gradient fills.
Source Firkin
Because I love dark patterns, here is Brushed Alum in a dark coating.
Source Tim Ward
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
One more brick pattern. A bit more depth to this one.
Source Benjamin Ward
A background pattern with green vertical stripes. A new striped background pattern. This time a green one.
Source V. Hartikainen
Orange-red pattern for tiled backgrounds.
Source V. Hartikainen
Heavily remixed from a drawing in 'Barbara Leybourne; a story of eighty years ago', Sarah Hamer, 1889.
Source Firkin
Background formed from the original with an emboss effect
Source GDJ
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
Zero CC Mossy stone tileable texture, photographed and made by me. CC0
Source Sojan Janso
This light blue background pattern is quite pleasing to the eye, it consists of a tiny rough grid pattern, which is seamless by design. That's it, if you like the color, you can use this seamless pattern in a web design without making any further modifications to it.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
A seamless canvas texture for using as background on websites. Colored in pale tones of brown.
Source V. Hartikainen
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Prismatic Isometric Cube Extra Pattern No Background
Source GDJ
Continuing the geometric trend, here is one more.
Source Mike Warner
Dead simple but beautiful horizontal line pattern.
Source Fabian Schultz
It has waves, so make sure you don’t get sea sickness.
Source CoolPatterns
Remixed from a drawing in 'Maidenhood; or, the Verge of the Stream', Laura Jewry, 1876.
Source Firkin