The great Catan iOS game has added in its first expansion, available via an in-app purchase, and it's based on the Seafarers of Catan expansion from the original German board game. The expansion introduces ships and shipping routes to the kingdom-building simulation, and it includes 10 different scenarios to build ships in, as well as pirates, a Gold River tile and some extra victory cards with different bonuses.
The expansion content is US$3.99 inside the app, but even if you don't want to shell out the extra four bucks, one of the scenarios is included, so you can at least see how it changes the game. The Catan app itself has been critically acclaimed, and I really like this model of releasing content -- it seems like a nice solid way of both making sure that content updates are significant improvements to an app, as well as allowing developers to get their own reward for releasing that content. Hopefully we'll see some more apps, outside of the board game model, take this approach in the future.