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.wrapper{
	width: 100%;
	text-align: justify;
	font-size: 0;
	font-size: 12px\9; /* IE6-9 only fix */
}

.wrapper div{
	display: inline-block;
	zoom: 1;
	*display: inline; /* IE stuff again */
}

.wrapper:after{
	content: "";
	width: 100%;
	display: inline-block;
	zoom: 1;
	*display: inline;
}

Source: http://code.jelmerdemaat.nl/examples/justified-grid-test/