Another trick I've seen that I wish I'd come across long ago - a particular use of IE conditional comments to avoid having to break out IE CSS fixes into different style sheets:

    <!--[if IE 6]><body class="ie ie6"><![endif]--><!--[if IE 7]><body class="ie ie7"><![endif]--><!--[if !IE]>--><body><!--<![endif]-->

This applies "ie" and version-specific classes to the body tag in IE browsers. Therefore, if something about a button tag doesn't look right in IE in general, I can use the ".ie button" selector to apply a fix right below my button styling. If it's just IE 6 giving me grief, I can use the ".ie6 button" selector.