Pattern #100! A black classic knit-looking pattern.
Source Factorio.us Collective
Prismatic Groovy Concentric Background 3 No Black
Source GDJ
Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
From a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin
Prismatic Isometric Cube Wireframe Pattern No Background
Source GDJ
A seamless web background with texture of aged grid paper.
Source V. Hartikainen
A seamless pattern created from a square tile. To get the tile, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This one is super crisp at 2X. Lined paper with some dust and scratches.
Source HQvectors
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Prismatic Geometric Pattern Variation 2 With Background
Source GDJ
Nicely crafted paper pattern, although a bit on the large side (500x593px).
Source Blaq Annabiosis
Dark squares with some virus-looking dots in the grid.
Source Hugo Loning
A free seamless background with pink spots.
Source V. Hartikainen
A large (588x375px) sand-colored pattern for your ever-growing collection. Shrink at will.
Source Alex Tapein
Colourful background achieved with gradient fills.
Source Firkin
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Tile available in Inkscape using shift-alt-i on the selected rectangle
Source Firkin
A lot of people like the icon patterns, so here’s one for your restaurant blog.
Source Andrijana Jarnjak
Seamless pattern the tile for which can be had by using shift-alt-I on the selected rectangle in Inkscape.
Source Firkin
Tile-able Dark Brown Wood Background. Feel free to use it as a background image in your designs or somewhere on the web. By the way, the color seems to be close to Coffee Brown.
Source V. Hartikainen
Here's a repeatable texture that resembles a light green concrete wall or something similar.
Source V. Hartikainen
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman