Derekovich,
Ещё вариант варианта выше )))
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style>
.float{height: 20px;background: yellow;margin-bottom:10px;}
.size{height:100px}
</style>
<script src="http://code.jquery.com/jquery-latest.min.js"></script>
<script>
</script>
</head>
<body>
<div class="float"></div>
<div class="float"></div>
<div class="float"></div>
<script>
var floats = $('.float');
$(document).click(function (event) {
$('.size').not(event.target).removeClass('size');
$(event.target, floats).toggleClass('size');
});
</script>
</body>
</html>