The four apps in my iPhone dock are the ones that I find myself using all the time: Speed Dial 1, Fahrenheit, Horizon, and Night Stand.
Speed Dial 1: I have it configured to call my husband with one click, so I can call him when I'm on my way home from work by just pressing the icon. That way I don't have to fumble around with finding him in my favorites list. I have an iPhone4, so I don't have Siri (yet). That's all it does, just calls one number, but it does it beautifully. If you want more than one speed dial button, you can download and install Speed Dial 2, 3 and/or 4. They come in different colors, and you can configure them in your iPhone settings.
Fahrenheit: A weather app (it also comes in "Celsius"). I actually like the looks of the Apple weather app better, but Fahrenheit stays in my dock because it shows the current temperature as a Badge App icon. According to Apple's weather app, it's always 73 degrees. That would be great, if it were true (currently it's 98 degrees here in Kansas City). Tapping on a day will give you an expanded forecast with lots of detail like sunrise, sunset, humidity, wind speed, etc. You can even press a button and get satellite maps and radar, although I never do.
Horizon: I recently started using a calendar app called Horizon. It interfaces with the iPhone calendars, and presents the information in a list. Clicking on a day gives you a weather panel with the date, the current temperature and weather condition, windspeed, humidity, and the precipitation possibility. It's a clean presentation, and easy to view in a hurry. You can edit calendar events through the app, but I find it a little fiddly, so I generally stick to iCal to add and edit events. The main point of the app is showing the weather for events, which would be even more useful for someone with a lot of sports events, for instance.
Nightstand: I've downloaded and tried a lot of clock apps, but Nightstand is the one I've stuck with. It has a really nice digital clock display, and I have it configured to show the day of the week and the weather conditions. There are several different themes, including analog and flip, but I like the soothing blue digital effect. I only use it as an alarm clock when I'm away from home, but I really like it for that. Propped up on a Wedge iPhone stand or the Teeny Tiny Thai Pad (okay, that's a bit of overkill, but isn't it beautiful?), I can see what the time is with a touch. I see that they have now upgraded the app to Nightstand HD 2, with more features, but the original is fine for me.
is an established author, holds the distinction of being one of the
first female bloggers on the web, and is Propaganda3's own Manager of