Well lots of things, check the specifications.
Box-sizing: There have been a long standing problem with the impractical w3c box model, which added borders width and padding to the width of the box. This makes sense, but is impractical in some layouts, especially percentage based layouts where you can't tell the browser to please subtract 1px from the width, so in worst case this would just push your columns around.
The w3c box model wouldn't be a problem if you could do something like
width: 90%-4px; But since you currently cant, and since support for
Box-sizing is limited, most simply avoid borders and padding, usually avoiding padding by using an additional wrapper, of about 98% width of its parent element.
word-wrap: Very useful feature, even though alternatives exist for older browsers, I.e. The well known cross-browser solution for pre elements.
Code:
white-space: pre-wrap; /* css-3 */
white-space: -moz-pre-wrap !important; /* Mozilla, since 1999 */
white-space: -pre-wrap; /* Opera 4-6 */
white-space: -o-pre-wrap; /* Opera 7 */
word-wrap: break-word; /* Internet Explorer 5.5+ */
A property like word-wrap has long been missed, all browsers should support this property.
Multiple backgrounds: Very useful, will most likely cut down on the divisions needed in highly graphical layouts.
Text-shadow: Less useful, but still worth to mention. Works in Safari last i checked.
So would it be worth to check out, or learn how to use these properties? Honestly, i see no reason why any serious web designer shouldn't know about them already. And that's just some of the properties i find the most useful, there are also properties used for multi-column layouts on the table.
But maybe you are stuck with your WYSIWYG editors, and it prompts you every time you use a property it doesn't know about.
BTW, i would rather use som Alpha Transparent png's, without applying the fix for earlier versions of IE, that is until the css3 property is supported, and i honestly find it very unprofessional by w3c and browser devs, that such properties, or equivalent ain't available yet.
Transparency would be an obvious design goal, and currently we have to fake it with images.
