:before and :after
Add content before or after all matching elements.

:focus, :hover, :active
States now supported for all elements.

display
Support for all table layout values: table-row-group, table-header-group, tablefooter-group, table-row, table-column-group, table-column, table-cell, table-caption.

outline
Color, style, and width of the outline frame.

quotes
Define what characters to use to bound quotes.

MSIE 8 joins the other major browser vendors in offering full support for the CSS 2.1 Specification.

:nth-child, :nth-of-type, :nth-last-of-type, :first-of-type, :last-of-type, :only-of-type

Color alternating rows in a table, items in a list, etc. With this addition in Firefox 3.5, Firefox now supports all CSS3 Selectors.

-moz-border-image, -webkit-border-image

Create complex borders using images.

-moz-box-shadow, -webkit-box-shadow, (*available in MSIE through Microsoftʼs DropShadow Filter)

Cast a drop shadow from most HTML elements. Accepts color, offset, blur radius, spread radius.

text-shadow, (available in MSIE through Microsoft Shadow and DropShadow Filter)

Casts a drop shadow from text and text-decorations. Accepts color, offset, blur radius.

@font-face (*MSIE supports .eot or .ote files only)

Ability to specify downloadable fonts for page rendering

@page, left, right, and first page selectors, page-break-inside, widows, orphans

Better control over printing with CSS constructs.

-webkit-gradient
Gradients, linear or radial, with key points and "color-stops" that work similarly to a Photoshop gradient.

-webkit-mask
Obscure areas of images before they are rendered. Accepts images, -webkit-gradient, svg, and more.

-webkit-box-reflect
Create reflections specified by a direction, offset, and -webkit-mask.

-webkit-transition
Smooth interpolation between two CSS states. Accepts properties to transition, duration, delay, and timing functions. DOM events are fired when transitions are completed.

-webkit-animation
Builds on transitions, adding the ability to specify a specific set of "keyframes".

-webkit-transform, -webkit-transform-origin, moz-transform, -moz-transform-origin
Translation, scale, rotation, and skew along any axis and around a specified origin, or manipulate directly using a transform matrix.

(*many effects are available in MSIE through Microsoftʼs Visual Filters)

(**The next build of Chrome may support many of the webkit based additions)

Define CSS colors with an alpha channel for transparency that is not inherited by child elements. See Andy Clarke’s screencast.

Specify multiple background images to one element.

(*Multiple background support has made its way into Firefox nightly builds. As to whether it will be supported in the final release of Firefox 3.5 is yet to be seen.)

Define named styles that correspond to alternate style sheets, allowing users to select one of several presentation styles for a page. MSIE 8 brings this feature to full support across all the major vendors.

Local storage for modern web applications.

video, audio

Standards-based elements that support multimedia playback, and better scripting control.

(*Support in Opera is only partial, and not yet confirmed.)

Upload multiple files through one input field. In the past, workarounds have typically been achieved using Flash or Java applets.

New element type for defining a form value using a slider.

ondragstart, ondrag, ondragenter, ondragover, ondragleave, ondragend, ondrop

API for interactive web interfaces which fire native drag and drop events in the browser. Additionally a dataTransfer object holds dragged data.

MSIE 8 now supports embedding namespaced elements in XHTML. SVG and MathML are two popular uses, which should now be easier to implement in all the major browsers.

Detecting network connectivity events within javascript.

(*MSIE 8 only supports ononline and onoffline events)

Client side communication through IFrames between documents from different domains with the postMessage method.

(*Supported in WebKit nightlies. May or may not make it into Safari 4)

Creating and interpreting Javascript objects through the parse and stringify methods of the JSON object.

querySelector, querySelectorAll (*not supported in MSIE 8)

Method for retrieving 1 or more DOM objects by CSS selector (the way your favorite javascript libraries already do)

Updates to the window.location.hash property (anchor links) are treated like "traditional" navigations – they donʼt break the back button.

Support added by MSIE 8 makes this a feature of all modern browsers.

Request data from a URL on an outside domain securely.

Run background script processes on a webpage without interfering with user input. Similar to threading.

(*Available in Chromeʼs latest developer release)

Images will more accurately reflect their representations in Photoshop.

WIA-ARIA is a W3C specification that makes modern Ajax web applications more accessible to people with disabilities.

Web applications can get a user’s location if a location provider is installed.

(*Geolocation is also available through the Google Gears plugin on several other browser platforms and legacy browser versions)

Ability to specify images as data inline in your style sheet. Typically used for small sprites in order to minimize HTTP requests, reducing overall load time. Now possible in all major browsers with the introduction of MSIE 8. Support for older browsers is available through Javascript.