When I buckled this summer and picked up an iPhone, I was pretty sure I was doing it mostly for the camera (image and video) and the seamless integration with a number of Google services. I haven't been disappointed on those fronts - but it's been the home automation on the iPhone that's most impressed me.
We moved to California after Google acquired FeedBurner, and the house we bought is in a new development where the builder (Lennar) installed solar panels in every new home. Included with the panels was monitoring by SunPower - for the last two years I've been able to log into SunPower's website to see how much energy we consume each day and how much we produce.
SunPower released an iPhone app - and it's fantastic. With one click, I can see how much energy we've consumed or produced for the current day/month/year. Hilariously, a few weeks ago our neighbors were walking by and we got to talking about our solar panels (they live in the same model house as we do, but their panels face a different direction due to the arrangement of nearby homes and we were wondering whose panels produced more energy). Robin pulled out her cell phone, and my neighbor's wife pulled out hers - both compared their system's data in real time. (We'd guessed correctly - the neighbors panels produce more energy per day than ours does. And if you're wondering if this was our quintessential only-in-California moment since moving back here in 2007, the answer is yes - yes it was.)
Aside from the eye candy, there's a practical benefit to the app: getting real-time insight into when your home's energy consumption spikes can drive radically different behavior: seeing just how many kWh the dishwasher consumes, or the washer/dryer (all of which are new and are as energy efficient as can be), helped us shift when we used them - thanks to PG&E, we're on a variable rate plan and spend dramatically less per kWh at night than we do during the day. Similarly, we were able to help show our kids the impact things like having the "big" TV on can have (the TV doesn't consume a lot of power, but the stereo that produces the audio sure does). One side effect? They are much more conscientious about when they play the Wii now. :)
Sonos app is a case where the iPhone app is dramatically better than the product it complements. I cannot rave about our Sonos system enough - though my post from a few weeks after we first got it still pretty much sums up how much I love it. A very minor quibble was the included remote - it's an impressive piece of hardware (it's connecting to the Sonos's private mesh network via WiFi to communicate with each music server), but the UI was frustrating. Searching was cumbersome, as there was no touch screen and you had to use the dial pad to scroll through to find each letter to type out a band name or song title.
The iPhone app, on the other hand, is perfect. From my iPhone, I have complete control over every Sonos zone in the house - and because it's a touch screen, typing in search queries is a breeze. I can control volume for any set of attached speakers, pick which music plays where, you name it - and unlike the bulky Sonos remote, the iPhone is easy to keep in a pocket - which makes switching from radio to Rhapsody to Pandora a snap.
Alarm.com has an iPhone app. The alarm company the builder contracted with uses Alarm.com for their Internet monitoring - and though I've used their website a couple times, it's never been that useful for me. But the iPhone app is simple, and useful: one tap to arm the system, one to disarm - and an ability to review past alarm events (arm/disarm by user, sensor activations, overrides, etc.).
I could see this being useful when needing to remotely disable the alarm (to let someone in, for instance) or to monitor alarm activity. On the feature request list, I'd love to see a status window that would show me which sensors were currently in the 'tripped' state (i.e., which windows/doors are currently open) - but I haven't yet poked around enough to see whether that's even possible. (Impressively, if your alarm has any video capabilities, the feeds from those cameras are viewable from the app.)
Last but not least is a nice app called DVR Lite - it's the free version of a for-pay app that's a third-party app built to control your Series III TiVo or TiVo HD. Once you enable network remote control on the TiVo (a feature I didn't even realize the TiVo supported), DVR Lite auto-detects any TiVos on the network and provides you with a fully functional remote for your TiVo:
One of the things that's nice here is, like with the Sonos app, the ability to type on the iPhone screen is far superior to TiVo's Kings-Quest-like up-up-right-right-right-select-down-down-left-left-left-left-select text entry for finding programs. Another nice time saver in DVR Lite is one-click access to TiVo's mobile interface, which makes one-off recording of shows easy (particularly when you're not home to do it on the TiVo directly):
I'm sure there are other apps I'm missing. One I stumbled on that I'll put on Robin's iPhone is the Comcast app (solely to make it easier for her to listen to voicemail at the house when she's not home). What other home automation apps should I know about?