Colourful background achieved with gradient fills.
Source Firkin
A nice looking light gray background pattern with diagonal stripes.
Source V. Hartikainen
Might not be super subtle, but quite original in its form.
Source Alex Smith
Gold Triangular Seamless Pattern No Background
Source GDJ
A seamless texture traced from an image on opengameart.org shared by Scouser.
Source Firkin
From a drawing in 'Gately's World's Progress', Charles Beale, 1886.
Source Firkin
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
One more updated pattern. Not really carbon fiber, but it’s the most popular pattern, so I’ll give you an extra choice.
Source Atle Mo
Smooth Polaroid pattern with a light blue tint.
Source Daniel Beaton
Nice little grid. Would work great as a base on top of some other patterns.
Source Arno Gregorian
From a drawing in 'Real Sailor-Songs', John Ashton, 1891.
Source Firkin
If you want png files of this u can download them here : viscious-speed.deviantart.com/gallery/27635117
Source Viscious-Speed
Prismatic Snowflakes Pattern 2 No Background
Source GDJ
Prismatic Groovy Concentric Background 3
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
Used correctly, this could be nice. Used in a bad way, all hell will break loose.
Source Atle Mo
Pixel by pixel, sharp and clean. Very light pattern with clear lines.
Source M.Ashok
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868.
Source Firkin
A large pattern with funky shapes and form. An original. Sort of origami-ish.
Source Luuk van Baars
With a name this awesome, how can I go wrong?
Source Nikolay Boltachev
Honestly, who does not like a little pipe and mustache?
Source Luca Errico
A version without colours blended together to give a different look.
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
Prismatic Abstract Geometric Background 3
Source GDJ