Race for the Galaxy. Although the only components in the game are the cards themselves, it plays out very similarly to worker-placement games like Agricola or Puerto Rico. In each round of the game, each player secretly chooses a single action - such as settling a new planet, exploring the galaxy (for new cards), constructing a development, producing resources, or selling those resources. All players play each of the chosen actions, but the one who chose it receives a significant bonus. Each planet and development gives the player certain advantages or abilities, and is also worth a certain number of victory points at the end of the game. Naturally, whoever has the most points at the end of the game wins.
Recently Temple Gates Games released an app version of this game for both Apple and Android, and I must say it's a hit. The app includes a nice, clean interface, some basic but appropriate music and sound effects, a surprisingly good AI, a quick three part tutorial, and a variety of ways to play the game - including against the AI, against other players online, or even as a "pass and play" option where you substitute your device for the game with multiple people around the same virtual table.
While $6.99 is a bit steep for an app, particularly when the two expansions will run you an additional $3.99 each, you're still getting pretty good value for your dollar. Games are quick enough that you can easily jam several in a short amount of time, or just squeeze one in while waiting for something else. At least on a tablet, the cards are easy to read even without zooming in on them, and each card includes helpful tooltips to help explain any card that seems unclear.
If you're a fan of the game, this should be a no-brainer to pick up.