Mirrored Squares@2X #124
 Dark  CC BY-SA 3.0

Did some testing with Repper Pro tonight, and this gray mid-tone pattern came out.

Source Atle Mo

 More Textures
Batthern #324
 Grid  CC BY-SA 3.0

Sometimes simple really is what you need, and this could fit you well.

Source Factorio.us Collective

Old Mathematics@2X #44
 Stripes  CC BY-SA 3.0

This one takes you back to math class. Classic mathematic board underlay.

Source Josh Green

Background pattern 117@2X #525
 Noise  CC 0

A seamless pattern drawn originally in Paint.net by distorting a slice of background pattern 116 and copying the resulting triangle numerous times.

Source Firkin

Diagonal Noise #181
 Fabric  CC BY-SA 3.0

A simple but elegant classic. Every collection needs one of these.

Source Christopher Burton

Background pattern 253 #2153
 Brown  CC 0

A seamless pattern created from a square tile. To get the tile, select the pattern in Inkscape and use shift+alt+i.

Source Firkin

Little Knobs #310
 Light  CC BY-SA 3.0

White little knobs, coming in at 10x10px. Sweet!

Source Amos

Iron Grip #587
 Dark  CC BY-SA 3.0

Sounds like something from World of Warcraft. Has to be good.

Source Tony Kinard

Colorful Floral Background 2@2X #488
 Dark  CC 0

Colorful Floral Background 2

Source GDJ

Bright Squares@2X #88
 Light  CC BY-SA 3.0

It’s okay to be square! A nice light gray pattern with random squares.

Source Waseem Dahman

Seamless Wood Pattern #889
 Wood  CC BY-SA 3.0

A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.

Source V. Hartikainen

Abstract Tiled Background Extended 11 #522
 Noise  CC 0

Abstract Tiled Background Extended 11

Source GDJ

Simple bump #172
 Dark  CC 0

A simple bump filter made upon request at irc #inkscape at freenode. Made a screen capture of the making here: https://youtu.be/TGAWYKVLxQw

Source Lazur URH

Cross Stripes@2X #48
 Dark  CC BY-SA 3.0

Nice and simple crossed lines in dark gray tones.

Source Stefan Aleksić