Remixed from a design seen on Pixabay. The basic tile can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Remixed from an image on Pixabay uploaded by Prawny
Source Firkin
Here's a bluish gray striped background pattern for use on web sites.
Source V. Hartikainen
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Fabric-ish patterns are close to my heart. French Stucco to the rescue.
Source Christopher Buecheler
A background formed from an image of an old tile on the New York Metropolitan Museum of Art website. To get the base tile, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
From a tile that can be had by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
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 textured paper for backgrounds. Colored in pale orange hues.
Source V. Hartikainen
ZeroCC tileable stone texture, edited from pixabay. CC0
Source Sojan Janso
More tactile goodness. This time in the form of some rough cloth.
Source Bartosz Kaszubowski
A rusty grunge background for websites. Feel free to use it in your site's theme.
Source V. Hartikainen
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
A pattern derived from repeating unit cells each derived from part of a fractal rendering in paint.net.
Source Firkin
The green fibers pattern will work very well in grayscale as well.
Source Matteo Di Capua
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Inspired by a drawing seen in 'City of Liverpool', James Picton, 1883.
Source Firkin
Prismatic Triangular Background Design Mark II 5
Source GDJ
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
Super simple but very nice indeed. Gray with vertical stripes.
Source Merrin Macleod