Illustrator

From Web Designer Wall...
This Adobe Illustrator tutorial will show you how to create an abstract art that can be used for wallpaper, website header or background images. It is fun and easy. You will learn how to use the Warp and Twirl tool to create abstract vector art in minutes. Users with basic skills should be able to handle this tutorial. To continue on this tutorial, you need Adobe Illustrator CS or above.

http://www.webdesignerwall.com/tutorials/illustrator-abstract-vector-art

Vectortuts+ has an interesting tutorial on how to make an iMac and Magic mouse in Illustrator... pretty clever.
This tutorial is about using Adobe Illustrator's Mesh Tool (U) and several basic techniques to create a vector style monitor and mouse, with a similar design as Apple's brand new iMac 27" with magic mouse. You can use these techniques to create other monitors and mouse designs as well. Let's get started!