Week Cal. The standard iPhone Calendar app is pretty good. But it lacks a weekly calendar view that I find very important. Week Cal by Wasabi is a s imple, inexpensive yet highly effective calendar app that fills this gap. It rides on top of your iPhone Calendar database, so it stays synchronized and up-to-date, but it provides greater flexibility and ease-of-use in accessing calendar information, I use it every day and highly recommend it.
Momento. One of the uses of a handheld device that I have struggled with for over 10 years is the personal diary/log. I've used built-in note-taking and document creation apps, web-portals, etc., but never really found the app that met my needs - so I was constantly flopping back and forth between online, handheld and hardcopy formats for this purpose. Then I found Momento. This is the newest app in my productivity suite but it is also the one I find I like the most. It imports (automatically) my Facebook, Blogger and Twitter feeds so my journal is synched with these sources of my thoughts and notes (a process I had previously had to do manually). The user interface is crisp, attractive, intuitive and functional. Integration of audio, image and video is the best I've seen. The only missing element I can see is rich text formatting. But given what I've seen from the developers at MomentoApp, I'm sure that's already in the works!
ToodleDo. This is my killer productivity app. Task lists have been a top use of all my PDA/smartphone devices, but none has given me the practical, effective use of ToodleDo. It does all the things a to-do list app should do and none of the things it shouldn't. It syncs perfectly with the web app and the web app fits perfectly into my productivity system. There is a 3rd party app that syncs ToodleDo (web app) with your Outlook Tasks. I used this for 2 years quite effectively, but not without issues. There would be regular mis-syncs so that tasks closed or altered on the ToodleDo web/iPhone app would not be updated on Outlook. Since I really only used Outlook Tasks as a way to drag-and-drop emails to my task list (i.e., Outlook Tasks was a one-way conduit for tasks into ToodleDo), this mis-syncing wasn't a big deal to me. However, I didn't like the "untidiness" of this behavior, so about a month ago, I abandoned Outlook Tasks altogether and instead of the "drag-and-drop" email-to-task process, I just forward the subject email to a ToodleDo email address which then automatically creates a ToodleDo task. This works perfectly and I don't miss Outlook Tasks at all.
Runkeeper. I love to run. I've got all the gadgets and gear to go with the sport, too. I've even got a great Garmin Forerunner wrist-GPS for tracking my runs with pace, distance, elevation and all kinds of data about my running. But over the past few months, I've found that I leave everything behind except my iPhone, earbuds and my Runkeeper app. It does essentially all the things I use the Garmin for - except I've already got the phone with me for music/audiobooks and it automatically uploads my run data to the Runkeeper web app for tracking - as well as posting a tweet about my workout. Runkeeper Pro was recently made available as a free app, so I now also enjoy the audio-prompts and feedback of the Pro version!
Tap-and-Track. I'm not a dieter, but I like to be aware of what I eat. I've been using Tap-and-Track for about a year to keep up with my eating habits and have found it to be easy to use and to have an exhaustive database of food information. I use it every day.
DocsToGo. One the ways Windows Mobile was ahead of the curve literally 10 years ago v. all the other competitors in both the PDA and smartphone categories was the implementation of handheld Office view/create/edit apps. In making the jump from Windows Mobile to other platforms, this was by far the biggest loss. Now, finally, iOS has, in DocsToGo, an application suite that adequately brings this capability to the iPhone. It works extremely well. It allows effortless sync with Box.net (among other web apps) which is what I use for moving, editing and accessing Office-based files from the web, my PCs and my iPhone.
Dragon Dictation. I've waiting years for voice recognition technology to get to a level of practical functionality - and it has taken years to get there. But the jump from Dragon's desktop software to an iPhone app happened almost overnight! And it works incredibly well. I use it for capturing actions, notes, messages and other brief information verbally when I've driving. The text transcription is very accurate and the app has great built-in tools to instantly turn a spoken message into an email, SMS, tweet/status or other text-based use.
Evernote. I'll a dmit that I have not been an easy convert to Evernote. I've used it off-and-on for about a year and have fallen in and out of "like" with it. I'm still not convinced, but am currently using it regularly. The web-clipping capability is, in my mind, it's biggest advantage. I use it regularly for that. However, for any sort of static reference material, I ultimately end up emailing the item from Evernote to Gmail and storing it there - deleting the Evernote item. I use it for capturing text and image notes for later editing and reference on the web app or iPhone, but still don't see it as a long-term repository/reference tool. It seems most its uses can be readily accomplished with email use - except for "dynamic" information that is frequently updated or changed. So this is what I'm using it for now. In this regard, the ubiquitous capture and access is a real advantage over other note-taking/data capture apps I've tried (including ToodleDo's notebook feature among others). I wrestle a bit, though, even in this use, with why I couldn't just spin up DocsToGo (which auto-syncs with my Box.net web app providing ubiquitous access as well). So I'm still experimenting.