SimCity may not have had the smoothest release—in fact, to say otherwise would be disingenuous as the game had one of the roughest releases in video game history, to date. That being said, things have calmed down since its launch and its developers appear to be on track to releasing new content for the game.
The first piece of content (at least outside of the pre-order packs) was sponsored by Nissan. It wasn't very popular with the fans, but being free as it was, there was little reason to complain about it.
Today, EA Maxis has released the game's first real DLC called the SimCity Amusement Park set. It allows you to turn your city into a giant amusement wonderland with nine rides which will, as the official press release notes, "make any Sim scream 'Wheeee!'"
Effectively, this'll allow you to turn your city into a giant theme park, not unlike Orlando, Florida and its host of amusement parks. Well, it'd be like Orlando, if the city were ten times smaller and constrained in size to that of SimCity's. Snap!