Not strictly seamless in that opposite edges are not identical. But they do marry up to make an interesting pattern
Source Firkin
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
This is so subtle: We’re talking 1% opacity. Get your squint on!
Source Atle Mo
A browner version of the original weathered fence texture.
Source Firkin
Simple wide squares with a small indent. Fits all.
Source Petr Šulc.
A playful triangle pattern with different shades of gray.
Source Dimitrie Hoekstra
Coming in at 666x666px, this is an evil big pattern, but nice and soft at the same time.
Source Atle Mo
A seamless web texture of "green stone".
Source V. Hartikainen
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Geometric Tessellation Pattern 3 No Background
Source GDJ
Seamless Prismatic Pythagorean Line Art Pattern No Background. A seamless pattern that includes the original tile (go to Objects / Pattern / Pattern To Objects in Inkscape's menu to extract it).
Source GDJ
From a drawing in 'An Old Maid's Love. A Dutch tale told in English', Maarten Maartens, 1891.
Source Firkin
Everyone loves a diamond, right? Make your site sparkle.
Source AJ Troxell
Oh yes, it happened! A pattern in full color.
Source Atle Mo
A blue gray fabric-like texture for websites. An yet another fabric-like texture. It has subtle vertical and diagonal stripes to it.
Source V. Hartikainen
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
I guess this one is inspired by an office. A dark office.
Source Andrés Rigo.
The original enhanced with some gradients.
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