A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
From a drawing in 'Navigations de Alouys de Cademoste.-La Navigation du Capitaine Pierre Sintre', Alvise da ca da Mosto, 1895.
Source Firkin
Not so subtle. These tileable wood patterns are very useful.
Source Elemis
A seamless pattern formed from a square tile. The tile can be retrieved by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Colorful Floral Background 3 No Black
Source GDJ
Black paper texture, based on two different images.
Source Atle Mo
Based from Design Kindle
Derived from an image that was uploaded to Pixabay by pugmom40
Source Firkin
A mid-tone gray pattern with some cement looking texture.
Source Hendrik Lammers
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
There are many carbon patterns, but this one is tiny.
Source Designova
A seamless pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
Number 3 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
I’m guessing this is related to the Sony Vaio? It’s a nice pattern no matter where it’s from.
Source Zigzain
Just to prove my point, here is a slightly modified dark version.
Source Atle Mo
The image depicts a Japanese Edo pattern called "kanoko or 鹿の子" meaning "fawn" which has a fur with small white spots.
Source Yamachem
A dark one with geometric shapes and dotted lines.
Source Mohawk Studios
Remixed from an image that was uploaded to Pixabay by Pixeline
Source Firkin
Snap! It’s a pattern, and it’s not grayscale! Of course you can always change the color in Photoshop.
Source Atle Mo
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin