The latest is called Pocket Universe [App Store link]. For the $2.99US price, your iPhone or iPod touch gets a star atlas of 10,000 objects, a guide to moon phases, a list of what's up on any particular night including meteor showers and any visible planets, as well as live links to astronomy news.
The app also includes an accurate rendering of the positions of the 4 easily visible moons of Jupiter, but your best bet in seeing a planet this time of year is Saturn which is high in the southeast.
As we move toward summer, more and more people will be heading outdoors. That makes it it is a great time to learn the constellations and be able to understand what you are looking at, as opposed to just wondering what that bright thing is.
A nice feature of the app is auto tilt, so when you are pointing the right direction, you can tilt the phone up to get a view higher in the sky and the star map will follow your tilt. If, as rumored, the iPhone adds some kind of direction finding compass, apps like this can be even more helpful as you turn and tilt, as the map should track your movements exactly.
Pocket Universe has a very clever locate feature, where you can select an object, and there are on-screen directions to take you to the object by superimposing arrows on the screen. This feature didn't always work perfectly. I asked the program to find Saturn. It told me to follow the arrows, but no arrows appeared. It seemed to work fine on other objects I was looking for, and Saturn was properly placed on the sky map.
How does this object compare to some of the competition? Quite well. It's reasonably priced, and with the live links it has some features the others don't have. I also recommend Distant Suns, Starmap, and Star Walk as worthy alternatives.
Here are some screen shots: