Graphics on a smaller scale is graphic signatures. Hence it can be attempted by beginners as well as experts in the fields. How about giving a list of the signatures that I found wonderful from among the millions. And if you want to learn more about them, follow the links or this forum:
LayeredgfxAbstract SignatureLearn how to create a detailed signature using several filters and effects.
Abstract Walkthrough
Luminescent LinesThis technique is fairly simple and is a great way to create an abstract wallpaper or looks good integrated into another image.
Abstract Background of Colored BarsShort but attractive way to create a graphic for backgrounds, wallpapers, greeting cards, designs, and all that other good stuff.
Leopard Aurora BorealisNot exactly the Mac OSX
Leopard aurora wallpaper, but great effects to create something simillar.
Space Lighting effectsHow to create a space scene with some nice Lighting Effects in 10 Steps.
Abstract image tutorial Create a beautiful and extraordinary effect with some simple steps.
Cool abstract backgroundCreate abstract background from bubbles and waves.
abstract signature
Abstract Summer IllustrationLearn to create an illustration picturing the summer.
Swoshy linesHow to make an abstract ribbon-like effect using only
Adobe Photoshop.
Abstract Energy LinesHow to create some energetic lines you can use to create more lively digital creations.
Easy Abstract Photoshop TutorialHow to create a very simple abstract shape using a few brushes and effects.
The lightning effect
Intense Solar Flare (Filter) Effect
Signature tutorial Movement
Abstract Art Piece: "Lonium"In this Photoshop tutorial we’ll be walking through the process of making an abstract artwork, using abstract 3D renders, textures, and more.
Light RaysCreate a fantastic light ray background texture
Abstract Background
Grungy Metal TextureHow to make some grungy metal with a star
Signature Backgrounds
Abstract Airbrushing
Wallpaper EffectThis tutorial walks you through steps in creating a warped effect that you can use to create artistic and profressional background and wallpapers.
Trendy Background TexturesSimple technique using brush strokes for making some trendy background
Digital Star Effect
Stripy Abstract WallpaperSimple effect that can come in really handy.
Magic light streak wallpaper in photoshop
Mac-type backgroundThis tutorial is about making a "mac" style background.
Colourful swirl
Colorful Tornado
Firey ExplosionSpice up your
space art with this explosive tutorial
Abstract Artsy Background 
Please comment on the post and the ones you liked the most.