A simple example on using clones. You can generate a nice base for a pattern fill quickly with it.
Source Lazur URH
This is a semi-dark pattern, sort of linen-y.
Source Sagive SEO
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Black paper texture, based on two different images.
Source Atle Mo
Based from Design Kindle
A grid of squares with green colours. Since the colours are randomly distributed it is automatically seamless.
Source Firkin
A pale orange background pattern with glossy groove stripes.
Source V. Hartikainen
Inspired by this, I came up with this pattern. Madness!
Source Atle Mo
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Remixed from a drawing in 'Hungary. A guide book. By several authors', 1890.
Source Firkin
A comeback for you: the popular Escheresque, now in black.
Source Patten
The classic notebook paper with horizontal stripes.
Source Are Sundnes
A seamless pattern of dark bricks. Maybe it's not very realistic, but it looks good in my opinion.
Source V. Hartikainen
A slightly grainy paper pattern with small horizontal and vertical strokes.
Source Atle Mo
Sort of reminds me of those old house wallpapers.
Source Tish
To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
The edges of all the red objects line up either vertically or horizontally, but it doesn't appear so. Made from a square tile that can be got by selecting the rectangle in Inkscape and using shift+alt+i.
Source Firkin
Same classic 45-degree pattern, dark version.
Source Luke McDonald
Prismatic Groovy Concentric Background
Source GDJ
A seamless pattern based on a square tile that can be retrieved in Inkscape by selecting the rectangle and using shift-alt-i.
Source Firkin
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
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