People seem to enjoy dark patterns, so here is one with some circles.
Source Atle Mo
The following repeating website background is colored in a blue gray color and resembles a concrete wall or something similar to it.
Source V. Hartikainen
Fix and cc0 to get the tile this is based on.
Source SliverKnight
I skipped number 3, because it wasn’t all that great. Sorry.
Source Dima Shiper
Recreated from a pattern found in 'Az Osztrák-Magyar Monarchia irásban és képben', 1882. To get the tile this is based on select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
This one is rather fun and playful. The 2X could be used at 1X too!
Source Welsley
A criss-cross pattern similar to one I saw mown into a sports field.
Source Firkin
From a design found in 'History of the Virginia Company of London; with letters to and from the first Colony, never before printed', Edward Neill, 1869.
Source Firkin
Medium gray pattern with small strokes to give a weave effect.
Source Catherine
A seamlessly tile-able grunge background image.
Source V. Hartikainen