I've managed to make the twenty-eleven comment bubble entirely CSS3, using this tutorial: http://www.sitepoint.com/pure-css3-speech-bubbles I'm sure the colours aren't right as I'm using it for my own design, but the bubble's there for you to use :)

gistfile1.css

p.comment-count {
	position: relative;
	width: 43px;
	height: 30px;
	text-align: center;
	line-height: 30px;
	background-color: #fff;
	-webkit-border-radius: 15px;
	-moz-border-radius: 15px;
	border-radius: 15px;
	color:#424242;
	font-size:14px;
}

p.comment-count:after {
	content: ' ';
	position: absolute;
	width: 0;
	height: 0;
	left: 10px;
	top: 29px;
	border: 4px solid;
	border-color: #fff transparent transparent #fff;
	-webkit-transform: skew(-30deg,0deg);
}