A seamless pattern based on a rectangular tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
Continuing the geometric trend, here is one more.
Source Mike Warner
No idea what Nistri means, but it’s a crisp little pattern nonetheless.
Source Markus Reiter
Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
Prismatic Abstract Geometric Background 4 No Black
Source GDJ
Got some felt in my mailbox today, so I scanned it for you to use.
Source Atle Mo
This metal background pattern resembles a metal plate with rivets. Solid rivets on a metal plate.
Source V. Hartikainen
Drawn in Paint.net and vectorised in Vector Magic
Source Firkin
Prismatic Curved Diamond Pattern 8 No Background
Source GDJ
Paper model of a tetrahedron. Modelo de papel de um tetraedro.
Source laobc
A simple circle. That’s all it takes. This one is even transparent, for those who like that.
Source Saqib
This ons is quite old school looking. Retro, even. I like it.
Source Arno Declercq
More Japanese-inspired patterns, Gold Scales this time.
Source Josh Green
A seamless green background texture. The image is distributed under a Creative Commons License (like all of the images here).
Source V. Hartikainen
Dare I call this a «flat pattern»? Probably not.
Source Dax Kieran
Sort of like the Photoshop transparent background, but better!
Source Alex Parker
The name alone is awesome, but so is this sweet dark pattern.
Source Federica Pelzel
A free black metallic background pattern. Here's a new pattern I made that looks metallic.
Source V. Hartikainen
A brown metallic grid pattern layered on top of a dark fabric texture. It should look great when using as a tiled background on web pages, especially blogs.
Source V. Hartikainen