CSS

selector {
    min-height: 200px;
    height: auto !important; /* IE6 will ignore !important */
    height: 200px;
}

/* version with underscore hack */
selector {
    min-height: 200px;
    height: auto;
    _height: 200px;
}

• Teaser Box: Flexible, Fixed width - one "as is" image and css background positioning
• Rounded corners in CSS - CSS only technique works with browsers that support the :before and :after pseudoelements.
• jQuery Corner - native border-radius rounding in browsers that support it (Firefox, Safari, and Chrome). So in those browsers the plugin simply sets a css property on the element. But in IE and for all browsers, choosing a pattern other than "round" requires the use of the "div stips" method.
• Nifty Corner Cube - Javascript, GNU GPL licence

Native support

-moz-border-radius / -webkit-border-radius
-moz-border-radius-topleft  / -webkit-border-top-left-radius
-moz-border-radius-topright / -webkit-border-top-right-radius
-moz-border-radius-bottomleft / -webkit-border-bottom-left-radius
-moz-border-radius-bottomright / -webkit-border-bottom-right-radius

html>body selector /* not for IE<=6 */
_property: value; /* for IE<=6 */
#property: value; /* for IE7 */