For those of you, like me, who have found that you have to still check user agent for compatibility issues, because features like Modernizr still don’t detect everything, here are your user agents for the modern IE browsers. (Note that this means server side detection of the browser abilities.)
IE 10, Desktop: Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; Touch; rv:11.0) like Gecko;`
IE 10, as Modern App Mode: Mozilla/5.0 (Windows NT 6.3; Win64; x64; Trident/7.0; Touch; rv:11.0) like Gecko;`
IE 9, Desktop: User-Agent Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)
IE Windows Phone 8: Mozilla/5.0 (compatible; MSIE 10.0; Windows Phone 8.0; Trident/6.0; IEMobile/10.0; ARM; Touch);`
IE Windows Phone 7.5: Mozilla/5.0 (compatible; MSIE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0);`
IE XBox One: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; Trident/6.0; Xbox; Xbox One);`
Note: none of the arm, Xbox, or Windows Phone can support Flash.