Rafel Ivgi has published an extensive list of IE8 XSS filter evasions.
"Aspect9 has discovered several vulnerabilities in Microsoft Windows
Internet Explorer 8.0 Beta 2. This new version of Microsoft's famous browser includes new security improvements such as a Cross Site Scripting(XSS) filter. This version also includes a new object that safely allows transferring data across domains, allowing them to interact with each other.
Additional Details: http://www.webappsec.org/lists/websecurity/archive/2008-12/msg00057.html