For me and my workflow, my t0-do list and scheduling items that need to be addressed is critical. I have found Things to be a fantastic tool to organize and prioritize my to-do list. It is very powerful and based on the Getting Things Done principles. I particularly like that I can create steps within projects and schedule certain items on certain days easily. I sync this app with Things on my laptop via the wireless. It is a little pricey compared to most apps $9.99 but well worth every penny for me.
WhatsApp uses wi-fi or your data plan to send text messages, photos, video, etc. to your contacts. Your phone number is your unique identifier so you have to have the right phone number in, inclusive of country code. It allows you to text anywhere in the world without international charges. It is now available on other smartphones besides just the iPhone which expands its use. It seems like several chat/texting apps are out there and probably work similarly. The trick is to get one and sell your friends on it so you don't have to pay for SMS messages. WhatsApp is a great bargain at .99.
Personal Finance by Pageonce
Personal Finance allows me to track all my credit cards, frequent flyer miles, and bills from a variety of sources in one place. It notifies me if too many credit card transactions occur in a day and notifies me of big charges. It consolidates utilities bills for a home in another location all in one place that is easy to view and keep abreast of what is going on. It saves me logging into many different sites. I really like being able to log in via the web on Pageonce and setup the accounts. Then I just view everything via the iPhone app. For this one, there is a premium version and a free one.
IM+: All in One Messenger
IM+ consolidates all my chats into 1 app. I can set it to stay logged in and receive push notifications for up to 18 hours. It is easy to use. Again, there are others out there but this is one I found that works well and meets my needs. There is a Lite version which is free. It has some limitations and I have found the normal paid version worth it although a little pricey at $9.99.
Dragon Dictation is from the makers of Dragon Naturally Speaking, a popular software package. This app converts your voice into text. It's very accurate and great for recording longer emails that I don't want to type on the phone or text messages when I can't type and need to send a quick note. This app is free.
If you look at the pictures in this post, you can see screenshots of my first 2 pages of apps which are the ones I use the most. For the most part, I like free or very cheap apps. I've listed some of the pricier ones here which is probably good my most expensive apps are the best. It means I chose well. Be strategic on your apps and try to read user reviews. And there does seem to be an app for nearly everything.
What your favorite apps? Add them to the comments...