Target ALL VERSIONS of IE

<!--[if IE]>
	<link rel="stylesheet" type="text/css" href="all-ie-only.css" />
<![endif]-->

Target everything EXCEPT IE

<!--[if !IE]><!-->
	<link rel="stylesheet" type="text/css" href="not-ie.css" />
 <!--<![endif]-->

Target IE 7 ONLY

<!--[if IE 7]>
	<link rel="stylesheet" type="text/css" href="ie7.css">
<![endif]-->

Target IE 6 ONLY

<!--[if IE 6]>
	<link rel="stylesheet" type="text/css" href="ie6.css" />
<![endif]-->

Target IE 5 ONLY

<!--[if IE 5]>
	<link rel="stylesheet" type="text/css" href="ie5.css" />
<![endif]-->

Target IE 5.5 ONLY

<!--[if IE 5.5000]>
<link rel="stylesheet" type="text/css" href="ie55.css" />
<![endif]-->

Target IE 6 and LOWER

<!--[if lt IE 7]>
	<link rel="stylesheet" type="text/css" href="ie6-and-down.css" />
<![endif]-->

<!--[if lte IE 6]>
	<link rel="stylesheet" type="text/css" href="ie6-and-down.css" />
<![endif]-->

Target IE 7 and LOWER

<!--[if lt IE 8]>
	<link rel="stylesheet" type="text/css" href="ie7-and-down.css" />
<![endif]-->

<!--[if lte IE 7]>
	<link rel="stylesheet" type="text/css" href="ie7-and-down.css" />
<![endif]-->

Target IE 8 and LOWER

<!--[if lt IE 9]>
	<link rel="stylesheet" type="text/css" href="ie8-and-down.css" />
<![endif]-->

<!--[if lte IE 8]>
	<link rel="stylesheet" type="text/css" href="ie8-and-down.css" />
<![endif]-->

Target IE 6 and HIGHER

<!--[if gt IE 5.5]>
	<link rel="stylesheet" type="text/css" href="ie6-and-up.css" />
<![endif]-->

<!--[if gte IE 6]>
	<link rel="stylesheet" type="text/css" href="ie6-and-up.css" />
<![endif]-->

Target IE 7 and HIGHER

<!--[if gt IE 6]>
	<link rel="stylesheet" type="text/css" href="ie7-and-up.css" />
<![endif]-->

<!--[if gte IE 7]>
	<link rel="stylesheet" type="text/css" href="ie7-and-up.css" />
<![endif]-->

Target IE 8 and HIGHER

<!--[if gt IE 7]>
	<link rel="stylesheet" type="text/css" href="ie8-and-up.css" />
<![endif]-->

<!--[if gte IE 8]>
	<link rel="stylesheet" type="text/css" href="ie8-and-up.css" />
<![endif]-->


Universal IE 6 CSS
Dealing with IE 6 and below is 
always an extra-special challenge. These days people are dropping support for it 
right and left, including major businesses, major web apps, and even 
governments. There is a better solution than just letting the site go to hell, 
and that is to server IE 6 and below a special stripped-down stylesheet, and 
then serve IE 7 and above (and all other browsers) the regular CSS. This is been 
coined the universal IE 6 CSS. 
<!--[if !IE 6]><!-->
  <link rel="stylesheet" type="text/css" media="screen, projection" href="REGULAR-STYLESHEET.css" />
<!--<![endif]-->

<!--[if gte IE 7]>
  <link rel="stylesheet" type="text/css" media="screen, projection" href="REGULAR-STYLESHEET.css" />
<![endif]-->

<!--[if lte IE 6]>
  <link rel="stylesheet" type="text/css" media="screen, projection" href="http://universal-ie6-css.googlecode.com/files/ie6.0.3.css" />
<![endif]-->
Hacks
If you must...
IE-6 ONLY
* html #div {
    height: 300px;
}
IE-7 ONLY
*+html #div {
    height: 300px;
}
IE-8 ONLY
#div {
  height: 300px\0/;
}
IE-7 & IE-8
#div {
  height: 300px\9;
}
NON IE-7 ONLY:
#div {
   _height: 300px;
}
Hide from IE 6 and LOWER:
#div {
   height/**/: 300px;
}
html > body #div {
      height: 300px;
}