I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Psychedelic Geometric Background No Black
Source GDJ
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
Prismatic Curved Diamond Pattern 7 No Background
Source GDJ
CC0 and a seamless pattern from a tile drawn in Paint.net .
Source SliverKnight
Small gradient crosses inside 45-degree boxes, or bigger crosses if you will.
Source Wassim
The unit cell for this seamless pattern can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
And some more testing, this time with Seamless Studio. It’s Robots FFS!
Source Seamless Studio
A dark background pattern/texture of a dimpled metal plate.
Source V. Hartikainen
You just can’t get enough of the fabric patterns, so here is one more for your collection.
Source Krisp Designs
Textured Red Brown Plastic, Free Background Pattern. Although there's already enough plastic in our lives, let's bring it to the web too.)
Source V. Hartikainen
From a drawing in 'Resa i Afrika, genom Angola, Ovampo och Damaraland', P. Moller, 1899.
Source Firkin
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
Free tiled background with colorful stripes and white splatter.
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A beautiful dark wood pattern, superbly tiled.
Source Omar Alvarado
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'At home', J. Sowerby, J. Crane and T. Frederick, 1881.
Source Firkin
Light honeycomb pattern made up of the classic hexagon shape.
Source Federica Pelzel
Formed by distorting a JPG from PublicDomainPictures
Source Firkin
The classic notebook paper with horizontal stripes.
Source Are Sundnes
Here's an yet another seamless note paper texture for use as a background on websites.
Source V. Hartikainen