Android TV Remote Control
These days we're starting to see more and more Android TV devices and Television sets. Whether that's the Nexus Player, NVIDIA Shield, a 3rd party box, or a Sony BRAVIA TV with Android TV built-in. If you have an Android TV device, control it with any Android smartphone or tablet with Google's own app.
Directly from Google comes Android TV Remote Control. It's pretty straightforward and simply works great to control Android TV devices. There's the usual up/down, select buttons, pause/play, home, a D-Pad for gaming, and a touchpad. Basically everything you'll need for Android TV.
While this app is great and extremely simple to use, it only works with Android TV over WiFi. So it's not as universal as the rest, but does what it's supposed to extremely well.