CSS (Cascading Style Sheets) are now important elements for any website design. CSS is simple way to style you sites 
font, colors, spacing etc. You don’t need to setup all this things again and again for all pages when you use CSS just call CSS file to all pages.
CSS files can be easily created on any text editor like Notepad but it not provide the best way to create CSS file. Here come CSS editors which cut your development time and provide all help to build CSS file easily. CSS editors are like WYSIWYG editor which let you know what you are doing it highlights the code and values to help you what you are doing.
Top 5 Free CSS Editors
Simple CSS runs on Macs, Windows and Linux. Simple CSS allows you to easily create Cascading Style Sheets from scratch, and/or modify existing ones, using a familiar point-and-click interface. With Simple CSS, you can manage multiple CSS projects and import your existing style sheets. Simple CSS supports CSS2.
TopStyle Lite is a free version of TopStyle. TopStyle Lite is simple CSS editor.
CSS is a simple, structured language which fits quite naturally into a grid. The Stylizer code grid is designed specifically for CSS, providing access to real source code while delivering significant productivity gains over a general-purpose text editor.
JustStyle CSS Editor is full-featured, yet easy-to-use, software for webmasters. It is a specialized style sheets development environment, featuring everything needed to develop and deploy cascade style sheets. JustStyle CSS Editor provides an interactive user interface and presents CSS properties in special wizards and generic value lists.
cssed is a small developer editor and validator, that tries to ease the CSS editing. It is an Open Source project. It features syntax highlighting, syntax validation, MDI notebook based interface, quick CSS properties and values insertion, auto-completion and dialog-based insertion of CSS complex values.
I use free PHP/HTML/CSS/JavaScript editor – Codelobster PHP Edition.
It also has HTML code Inspector like FireBug has.