Material Design apps? Material Design apps.

1. Documents: Remember those brilliant mockups in the Material Design guidelines that Google didn't bother to implement? ^{^} This app looks exactly like how it was in the guidelines. It's a little low on features currenly but is constantly being updated. Kudos to the dev.
2. imago: An Imgur client. Alternative would be Open Imgur which is open source.
3. Clip Stack ✓ Clipboard Manager: A nice, free, ad-free, open source clipboard manager.
4. Skin Editor for Minecraft PE: You can build your own skin, or import a skin from a Minecraft PC account. I took /u/sethbling's Mario skin. Requires Block Launcher.
5. Flush - Public Toilet Finder: Bladder about to burst? You can find a washroom close to you, and add washrooms to the database to help others.
6. Material Urban Dictionary: Find out the meanings of swag and yolo in style.
7. Taggr ‐ Music Tag Editor: A brilliant ID3 tag editor, can also add album art to songs.

My source of these excellent apps is this G+ community. Do check it out.

Other brilliant non-Material apps:

1. Intugame VR: Play your PC games on Google Cardboard. Go through the app description carefully as you need to install some stuff on your PC.
2. Whatstat ROOT: Some nice stats about all your WhatsApp conversations. Root is required.
3. Chain Reaction: A fun game to play when with many people in the same room. It's under 200 KB in size. Not responsible for breaking friendships though lol.