Not so subtle. These tileable wood patterns are very useful.
Source Elemis
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
Prismatic Groovy Concentric Background 5
Source GDJ
"Beige Stone", Tileable Texture.
Source V. Hartikainen
Prismatic Hypnotic Pattern No Background
Source GDJ
Formed from decorative divider 184 in paint.net. Vectorised with Vector Magic.
Source Firkin
From a drawing in 'Cassell's Library of English Literature', Henry Morley, 1883.
Source Firkin
You know you love wood patterns, so here’s one more.
Source Richard Tabor
Nothing like a clean set of bed sheets, huh?
Source Badhon Ebrahim
Black brick wall pattern. Brick your site up!
Source Alex Parker
A background pattern inspired by designs seen in 'Burghley. The Life of William Cecil', William Charlton, 1857.
Source Firkin
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
Gold Triangular Seamless Pattern No Background
Source GDJ
Abstract Tiled Background Extended 6
Source GDJ
A free grid paper background pattern for using on web sites.
Source V. Hartikainen
A dark brown fabric-like background texture with seamless pattern of winding stripes.
Source V. Hartikainen
Subtle scratches on a light gray background.
Source Andrey Ovcharov
Seamless pattern made from a tile that can be obtained in Inkscape by selecting the rectangle and using shift+alt+i.
Source Firkin