If you're on Twitter and follow a lot of people then you know how hard it can be sometimes to catch up and keep up. TweetDeck is the solution. TweetDeck allows you to sort your feed into multiple columns and then file the people you follow into the columns for easier sorting. TweetDeck can connect to Twitter, Facebook, Google Buz
z, Foursquare, LinkedIn, and Myspace. No more needing to check sparate apps or webpages for all your friends updates. TweetDeck puts them all in one, easy to configure, dashboard on both your iPhone and they also have Desktop versions.
Need to write a quick note while you're out somewhere? Want to take a picture and remember where something was? Need to quickly dictate some notes to write up or remember later? Then Evernote is a solution for you. Evernote is a free service* that allows you to create those types of Notes and reminders that are then sync'd with their server and then sync'd with your home Mac or PC if you use their Desktop version. Its like having all your important notes, reminders, and lists in one location reachable from where ever you happen to be.
*Premium also available for more bandwidth and storage
If you Geocache then the Official Geocaching App ($9.99) is a must for you. Its a
full featured Geocaching application with the ability to pull up nearby caches, load pocket queries, view cache details, and see posted pictures. Once you've picked a cache to try it can use the iPhone's built in GPS and Compass (3GS and 4 only) to guide you right to the cache location. Then when you've found the cache you can log field notes and directly upload them as your log to the Geocaching site logging your find in your profile.
If you're a runner you might like MapMyRun+ ($4.99) [or the free MapMyRun] MapMyRun tracks your running by plotting your path on the map using the
iPhone's built in GPS. The app keeps up with your current and average min/mile, average speed, and your start and finish times. When finished with your run you can then choose to make the run Public or Private by uploading it to their server to share with your friends. It also has the ability to send updates to your Twitter or Facebook page. They have various levels of accounts on the MapMyRun site but I've been quite happy with the free account type. I did upgrade to the MapMyRun+ app instead of the free MayMyRun so I could get in-app music controls but that's not necessary if you don't listen to music when you run. They also have a MapMyRide application for bike riders that want to do the same tracking.
NOTE: Thanks Dave for the recommendation on this app. I use it every run and am loving it.
Ever been out at a store and see something you want and have this nagging feeling you've seen it cheaper somewhere else nearby? Redlaser can help. Redlaser uses the iPhone's camera to snap a picture of the items barcode then it deciphers the data and performs an online search for that exact same item. It then shows you the prices of the same item online as well as nearby locations that it can find a price for (based on your location). I mainly use it for remembering stuff that I know I want to order online rather than pay an overpriced fee in a store. Redlaser has saved me tons of money since it came out.
NOTE: Redlaser was recently purchased by e-bay so what is to become of it and what its features will mutate into are yet to be disclosed by e-bay.
If you're into Instant Messaging and want to still be able to IM your friends while you're on the go then its worth the $9.99 to get BeeJiveIM for the iPhone. BeeJiveIM was one of the first to take advantage of Apple's Push service and allow your application to be closed yet still receive notices when your friends IM you. BeeJiveIM is a full featured IM Client allowing you to set up all of your accounts into one IM Client instead of multiple clients. With just this one client you can IM with your AOL, YIM, MSN, etc... friends while on the go.
Of course your iPhone wouldn't be complete without the Official Facebook App.
Gain full access to your Facebook profile and friends. Upload pictures, update your status, send and receive messages, respond to friend request, and comment on friends pictures and post. All the features of Facebook are available on the website are available in the application. A must have for Facebook junkies :)
These are just a few of the slew of applications that I have on my iPhone4 today. Mashable has a huge list of over 700 app reviews that you might also find useful for categories I did not cover. Feel free to hit me up if there is a particular app type you are looking for and I'll be glad to recommend what I use for that need (if I have one) or I'll do some searching and find one to fit your needs and let you know what to try.