Here is a state of my iPhone article which lets you know about some applications you may want to consider and some you may not.
Fring: This wonder-software allows the iPhone/iPod Touch to stay connected to people on various communications networks from Skype to MSN Messenger. In reality, as amazing as this software is, the voice quality on Skype calls is pretty poor on most every call I have tried. Perhaps this is just my phone but who knows. Still, the ability to send text messages on various networks is a useful addition to the Apple device. Keep in mind however that there may be some delays using Fring and you have to keep the program in the foreground to use it effectively or jailbreak your iPhone so you can run this program in the background.
TouchType: The latest version has spell check and lets you save entries as virtual email templates, allowing you to quickly email frequently used text to others via your pocket-sized Apple device. In practice the program although only $.99 is buggy and spell check frequently locks up my phone. When it works, it does so very well.
NYTimes: Great software - it lets you experience the news virtually in an easy to use fashion.
Bloomberg: Great software and it allows for pretty good stock charts as well as access to a wealth of general and financial news.
Pandora: I still love this software and with a connection to your car's stereo system you may find that Pandora on an iPhone has better connectivity that Satellite radios which seem to lose signals (especially Sirius) whenever you go near trees or under bridges.
Lightsaber: This is a distraction which turns your iPhone into a virtual light saber - from Star Wars. This will appeal to serious Star Wars fans and is free.
Sticher Radio: Another free app which is more or less a wireless podcast conduit letting you listen to various types of audio content from news to finance, sports and just about anything else.
AP Mobile News Networks: Great app - free and complete access to lots of news.
Easy WiFi: At a cost of $1.99 this software allows you to rapidly connect to various WiFi networks around the world. It is good and the tech support is second to none. I did find that not all networks are in the system but the software is a time-saver and especially helps when you are looking to quickly connect to a nearby access point.
SnapTell: Take a picture of a CD or DVD cover and find it online and then buy it immediately. Amazing software which could come in handy at some point.
FS5 Hockey: Free software which transforms your phone into a virtual air hockey game. It is pretty good and a great diversion.
Digg: The app is similar to the web version but not as fully functionally.
Scribble: A great app that is free and lets you turn your iPhone into a piece of paper and a bunch of markers. If you like to doodle or have a kid that does, this software is a lifesaver at restaurants where kids tend to lose patience while waiting.
BubbleWrap: Turn your iPhone into bubble wrap and waste hours of time.
Google Earth: This iPhone version is pretty neat and has some added functionality beyond the web version.
MoMemory: A great game of electronic concentration.