remove entry-title vertical space

In your style.css, you have this CSS rule:

.singular .entry-title {
	color: #000;
	font-size: 36px;
	font-weight: bold;
	line-height: 48px;
}

The .singular .entry-title selector targets the entry title for single post pages. It is overriding the default line-height rule for entry-title of 1.5em:

.entry-title {
	clear: both;
	color: #222;
	font-size: 26px;
	font-weight: bold;
	line-height: 1.5em;
	padding-bottom: .3em;
	padding-top: 15px;
}

Since TwentyEleven doesn’t have a custom CSS option, you can either create a child theme to add the following CSS rule, or use a plugin like Lazyest Stylesheet or Custom CSS Manager.

.singular .entry-title {
	line-height: 1.5em;
}