Online Tools

Code Validation

The W3C HTML Markup Validation Service
The W3C CSS Validation Service
Living HTML5 Validator

Color Mixers

Color Picker
Color Schemer
HSL Picker
Color Blender Tool

Color Palettes

ColourLovers
Adobe Kuler
Color Scheme Designer

Fonts

Google Fonts
Font Squirrel
Font Zone

Graphic Tools

Dynamic Drive: Favicon Generator

Tablet & iPhone Emulators

iPad Peek
iPhoney: iPhoney emulator

Text Convertors

ASCII Text to Hexadecimal text

Advance CSS tools

Ultimate CSS Gradient Generator
Flexy Boxes
Border Image Tool