Awesome
idea-markdown
Markdown language support for IntelliJ IDEA, RubyMine, PhpStorm, WebStorm, PyCharm, AppCode and Android Studio.
This plugin is no more maintained and it has been removed from Jetbrains plugins repository. There is a Markdown plugin officially supported by Jetbrains.
This plugin is based on the excellent PegDown library by sirthias. Greetings also to JetBrains for giving away free licenses for IntelliJ IDEA for this project contributors.