HTML5 Boilerplate
HTML5 Boilerplate provides a great way to get started building HTML5 sites. It includes many best practices out of the box and even includes a few tricks that many people don’t even know about. The custom download option allows you to pick the features that you want to include in the files that’s generated. You can read more about it here.
Initializr
Although HTML5 Boilerplate provides a great foundation for starting HTML5 sites, it focuses on providing a starting shell structure (namely an html page, JavaScript files, and a CSS stylesheet) and doesn’t include much in the way of page content to get started with. Initializer builds on HTML5 Boilerplate and provides an initial test page that can be tweaked to meet your needs. It also provides several different customization options to include/exclude features.
CSS3 Maker
CSS3 provides a lot of great features ranging from gradient support to rounded corners. Although many of the features are fairly straightforward there are some that are pretty involved such as gradients, animations, and really any styles that require custom vendor extensions to use across browsers. Sure, you can type everything by hand, but sites such as CSS3 Maker provide a visual way to generate CSS3 styles.
CSS3, Please!
CSS3, Please! is a code generation tool that can be used to generate cross-browser CSS3 styles quickly and easily. All of the main things you can do with CSS3 are available including a clever way to visually generate CSS3 transform styles.
Ultimate CSS Gradient Generator
CSS3 Maker (above) has a gradient generator built-in but my favorite tool for creating CSS3 gradients is the Ultimate CSS Gradient Generator. If you’ve created gradients in tools like Photoshop then you’ll love what this tool has to offer especially since it makes it extremely straightforward to work with different gradient stops.
@font-face Fonts
Although @font-face has been available for awhile, I think fonts are cool and wanted to mention a site that provides a lot of font choices. When used correctly fonts can really enhance a page and when used incorrectly (think Comic Sans) they can absolutely ruin a page. Several sites exist that provide fonts that can be used with @font-face definitions in CSS style sheets. One of my favorites is Font Squirrel.
HTML5 & CSS3 Support and Tests
Interested in knowing what HTML5 and CSS3 features a given browser supports? Want to know how various browsers stack up with each other as far as HTML5/CSS3 support. Look no further than the HTML5 & CSS3 Support page or the HTML5 Test page.
CSS3 Easing Animation Tool
CSS3 animations aren’t widely supported across browsers right now (I’m not really using them at this point) but they do offer a lot of promise. Creating easings for animations can definitely be a challenge but they’re something that are critical for adding that “professional touch” to your animations. Fortunately you can use the Ceaser CSS Easing Animation Tool to simplify the process and handle animation easing with…...ease.
There are several other online tools that I like but these are some of the ones I find myself using the most. If you have any favorite online tools that simplify working with HTML5 or CSS3 let me know.
http://weblogs.asp.net/dwahlin/a-few-of-my-favorite-html5-and-css3-online-tools