Mastering frequently used applications increases the productivity significantly.
Controlling these applications via keyboard is a part of this "mastering process" which helps you use an application with 2 hands = much faster.
Also, knowing the tricks of tools inside these products definitely opens new doors for creating.
Specifically for 
designers, here is a 
list of cheat sheets for the most popular applications like 
Photoshop, 
Illustrator, 
Gimp, 
Fireworks & more..
 Keyboard shortcuts
Keyboard shortcuts are very well organized, both by menu & alphabetically.
Also, shortcut presets that add lots of extra shortcuts are provided too.
Keyboard shortcuts for previous Photoshop versions:

There are many different way & settings for converting images to 
black and white with Photoshop.
This is a Photoshop file presenting different filters/presets. Just update 1 file & see the various outputs.

A compact & helpful guide on 
Photoshop’s brush tool.
 
Adobe Illustrator CS4 Shortcuts (Mac - PC)
 For the previous versions of Illustrator:
For the previous versions of Illustrator:
- Adobe Illustrator CS3 Shortcuts (Mac - PC)
- Adobe Illustrator CS2 Shortcuts (Mac - PC)
Adobe InDesign CS4 Keyboard Shortcuts (Mac - PC)
 For the previous versions of InDesign:
For the previous versions of InDesign:
- Adobe InDesign CS3 Shortcuts (Mac - PC)
- Adobe InDesign CS2 Shortcuts (Mac - PC)
QuarkXPress 8 Keyboard Shortcuts (Mac - PC)
 For the previous versions of QuarkXpress:
For the previous versions of QuarkXpress:
- Adobe QuarkXPress 7 Shortcuts (Mac - PC)

The 
Adobe pen tool works similar in Photoshop, Illustrator and InDesign. Tips & tricks on using this powerful tool.
 And more on Gimp:
And more on Gimp:
Fireworks CS3 Quick Reference (Mac - PC / direct link to PDF file )
 Quick references for previous Fireworks versions:
Quick references for previous Fireworks versions:
- Fireworks MX quick reference (Mac - PC)
- Fireworks 4 quick reference (Mac - PC)

Computer Arts presents 
keyboard shortcuts for Freehand MX, 3D Studio Max, Illustrator, InDesign & Photoshop.
 Keyboard shortcuts for previous versions of 3D Studio Max:
Keyboard shortcuts for previous versions of 3D Studio Max:
 
