Android: If you like writing in Markdown (and you should), Draft is a great note taking app for Android with Dropbox syncing and a clean interface.
There are lots of Android note-taking apps, but Draft offers a solid suite of features that make it worth the price tag. The app has full Markdown support, and will preview your rendered notes in the app's main screen. If you're a little rusty using the language, the app also adds a custom row to your keyboard to automatically format text and create lists with proper syntax. Beyond that, it also syncs your notes on Dropbox, and since they're all in plain text, you can open them with any text editor, on any platform. My favourite little touch is the ability to add a new quick note from your main index page, without jumping into a full screen editing window.
Obviously, Draft has its competition, but if you value a clean interface, Markdown support, and creative touches from developers, it's well worth a look.