The App Store is home to a huge number of ports, from an array of retro games to customized versions of open source titles like Battle for Wesnoth [$4.99 - iPhone / iPad] and Frogatto [$4.99]. Recently three more ports made their way to the iOS family of devices, and while I didn't think any of them were that great, they have enough notoriety behind them that surely someone will be interested.
Gorillaz - Escape to Plastic Beach, $1.99 [iPhone / iPad] - To go with their recent album release, the Gorillaz have created a three episode online game. The first two episodes are Flash based and free to play, while the third chapter has been developed in Unity and is pay to play for both the iPhone and the Unity browser plugin. It's hard to say which is the port, but the iPhone version sports tilt controls. Curiously enough, there's also an iPad version of the game for the same price, which has left me scratching my head as to why they didn't just make the whole game universal.
Gameplay is similar to that of Glu's Glyder [99¢ / Free] and Glyder 2 for the iPad [Free] in that you're just flying around through hoops and updrafts completing various objectives. If you're a Gorillaz fan the game might be worth checking out because they do a decent job of recreating the cool Gorillaz universe from the music videos, but if the Gorillaz don't do much for you, neither will escaping to Plastic Beach.
Somersault, $5.99 - Using the same Unity browser plugin from the Gorillaz game you can try out the first level of Somersault online for free. The computer game has won some awards and developers are calling Somersault the "indie game of the year". I'm not sure I'd go that far, but at least the control mechanic of using your finger to draw lines for your little guy to bounce off of works much better on the iPhone than it does on the computer with a mouse.
Somersault has some nice level design, and it's pretty cool how they managed to turn the "draw lines to bounce things" control mechanic in to an entire adventure game. The developers are also very active in our forums, which is always a good sign. If the above trailer looks at all interesting to you, at least give the free versions a try.
Furcadia, $4.99 - First going online in late 1996, Furcadia was among the first games available when MUD's were beginning to get graphical interfaces and turn in to MMO's. The game features highly customizable anthropomorphic animals for avatars, and much like Second Life focuses on user-generated content. These player driven parts of the virtual world are called "Dreams," and even though Furcadia seemed pretty lame when it was first released compared to other games of its day like Meridian 59 or Ultima Online, the art editor, map creator, and scripting language called "DragonSpeak" was totally ahead of the time and was basically duplicated 7 years later in Second Life.
While the iPhone client costs $4.99, Furcadia is completely free to play and you can download the Mac and PC client for free if you want to give the game a try. I'm not entirely sure how much (if any) interest most people will have in Furcadia on the iPhone, but if you remember hearing about the game 15 years ago, it was fairly cutting edge. If you would have told me in the 90's that the game would one day be playable on mobile phones, I would have never believed you-- What's even more amazing is there are still thousands of people online in game.