Here's a subtle marble-like background for use on websites.
Source V. Hartikainen
High detail stone wall with minor cracks and specks.
Source Projecteightyfive
Looks a bit like concrete with subtle specks spread around the pattern.
Source Mladjan Antic
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
A seamless background texture of old cardboard.
Source V. Hartikainen
By popular request, an outline version of the pentagon pattern.
Source Atle Mo
Prismatic Snowflakes Pattern 3 No Background
Source GDJ
The image depicts a seamless pattern of Japanese Edo pattern called "kikkou-matsu" or "亀甲松" meaning " tortoiseshell-pinetree".The real pinetree is like this: https://jp.pinterest.com/pin/500744052301065077/
Source Yamachem
This texture looks like old leather. It should look great as a background on web pages.
Source V. Hartikainen
Dark blue concrete wall with some small dust spots.
Source Atle Mo
Otis Ray Redding was an American soul singer-songwriter, record producer, arranger, and talent scout. So you know.
Source Thomas Myrman
Greyscale version of a pattern that came out of playing with the 'light rays' plug-in for Paint.net
Source Firkin
Floral patterns might not be the hottest thing right now, but you never know when you need it!
Source Lauren
Prismatic Curved Diamond Pattern 2 No Background
Source GDJ
Turn your site into a dragon with this great scale pattern.
Source Alex Parker
A seamless dark leather-like background texture with diagonal lines that look like stitches.
Source V. Hartikainen
From a drawing in 'Hubert Montreuil, or the Huguenot and the Dragoon', Francisca Ouvry, 1873.
Source Firkin
Prismatic Geometric Pattern Background 2 No Black
Source GDJ
ZeroCC tileable moss texture, photographed and made by me. CC0
Source Sojan Janso
Luxurious looking pattern (for a T-shirt maybe?) with a hint of green.
Source Simon Meek
A seamless light gray paper texture with horizontal double lines.
Source V. Hartikainen