Ingress: An augmented reality MMO GPS game. You walk around IRL, capturing pieces of public art or local landmarks (portals) and link them together with keys to create triangular fields, claiming territory for the faction you're a part of. It's good exercise, and a fun way to meet other people and explore your city.

It's consumes a massive amount of data and battery though. That, and some stalking/camping tactics from some opposing locals in my area have blunted my interest somewhat, so I'm not terribly active anymore. I still participate in the big organised events and farm items for the newer players.

QuizUp: Trivia game where you're paired up against a random player and take them on in a topic of your choosing. You earn experience by answering correctly and quickly and beating your opponents, and if you're really into a topic, you can check yourself out on the global and national leaderboards.

I was ranked first in the world in Final Fantasy for about a month before I was overtaken by some people who I suspect paid for XP boosters.

Flappy Bird: Yeah, I haven't uninstalled this.