Tools | CSS Cookbook, 2nd Edition

http://www.browsercam.com/: BrowserCam is an affordable, web-based service that tests a web design in multiple browsers on numerous operating systems. At the time of this writing, a free 24-hour evaluation period is available for web developers that register onto the site.

http://www.danvine.com/icapture/: A free tool for web developers to preview web pages as viewed in Safari. A great site for Windows users when the only Macintosh product they want to buy is an iPod.

http://gallery.theopalgroup.com/selectoracle/: A free service designed to help people learn more about complex CSS selectors by translating their meaning into plain English. CSS selectors can be submitted in one of two ways. The first method is to copy and paste a CSS selector into a form on the web site. The other method is to enter either a URL of a web page with an embedded style sheet or a URL to an external style sheet. The service then renders the CSS selector into easy-to-understand language.

http://jigsaw.w3.org/css-validator/: This free service, provided on the W3C server, checks CSS for proper structure. You can test your markup by uploading files, entering a web address in the form, and then copying and pasting the CSS into a form field. And if you are so inclined, you can download and install the validator on your own server.

http://validator.w3.org/: The W3C HTML validator is another free service from the W3C. Similar to the CSS validator, the HTML validator checks to see if your markup conforms to web standards.

https://addons.mozilla.org/extensions/moreinfo.php?id=60: Chris Pedrick has created an indispensable extension for the popular Firefox and Mozilla browsers. A few features involve editing a web page's CSS through the browser, sending a web page's code directly to a W3C's validator, placing an outline on block level elements, as well as many, many other functions with a simple click of the mouse.

http://www.culturedcode.com/xyle/: Xyle scope is an indispensable tool that helps people of all skill levels. Accepting either a link to a web site or pulling up a web page from your computer, Xyle scope allows developers to see how the markup and CSS work together to build a web page design. Since the software is tied to the Web Kit, Safari's rendering engine, it is only available for Macintosh operating system.