Microsoft has just launched a new website called modern.IE that provides a suite of tools to help developers test their websites.
The website integrates a scanning feature that let's you enter your website's URL and it will analyze its contents against a variety of best practices (not only pertaining to IE, but also general concerns).
The analysis tool checks for things like...
The nice thing about the tool is that it not only finds suggestions, but it also recommends ways to resolve the issues it finds. In addition it doesn't just point out IE specific stuff, but also about more generic concepts like using CSS3 vendor prefixes and to consider responsive web design.
Microsoft understands that not all developers use Windows when they develop and have Internet Explorer easily available in order to test. So, a special 3 month free testing account is available with BrowserStack.
In addition, Microsoft is providing free Virtual Machine images for you to use if you want more control. Even though BrowserStack is awesome for a quick sanity check or to run unit tests, if you are trying to debug something having a local VM is optimal in those cases.