One of the more interesting things you can do with the iPhone is use it as a remote control for other devices. Since the iPhone App Store launched almost two years ago, developers have created hundreds of remote control applications.
Some of them are for entertainment - designed to control A/V equipment in your living room. Others control household appliances, functions on your computer, or even expensive corporate security systems.
For now, most remote control apps operate over the Internet, or via a Wi-Fi or Bluetooth link between your iPhone and another device. But one company is developing an infrared iPhone accessory, which will open the doors for even more remote control applications.
It's conceivable that, with these apps and accessories, an iPod touch could replace the fanciest of universal remotes, and have the bonus of shipping with a Web browser and all the other apps on the App Store.
Via Apple's free Remote app, search and change the song playing on your computer's iTunes jukebox from bed, across the house, or even outside. Or change volume settings, or hit pause, etc.
Another app called PodLink ($3.99) lets you wirelessly control music playing on another iPhone or iPod touch, perhaps one that is being played in a docking station across the room.
There's also a $4.99 app to control WinAmp if you use that.
Mouse and keyboard
This is helpful if you want to kick back and don't have a wireless keyboard, or if you're using an old computer hooked up to your TV and want to access the cursor or type something from the couch.
Several Blu-ray discs include Internet features that can be accessed via iPhone apps. For example, the free "pocket BLU" app can act as a remote for Blu-ray discs that support "pocket BLU" - including Bruno, Funny People, other movies. Features include controlling playback, browsing through chapters, the soundtrack, etc.
Other Blu-ray remote apps are available for different systems, including the Sony PS3.
Apple's $1.19 Keynote remote lets you control Keynote presentations if you own the iWork suite.
Other apps, like Evan Schoenberg's versatile $1.19 Rowmote can steer PowerPoint slides.
Desktop PC or Mac
This one takes a little tinkering, but free VNC - "virtual network computing" - remote desktop software on your computer (Mac, PC, Linux, etc.) will let you view and control it from anywhere, provided it's turned on and hooked up to the Internet.
If you have a SlingBox - a device designed to let you watch your home TV/cable service from anywhere, over the internet - you can use your iPhone to watch TV.
The $36.99 SlingPlayer Mobile app recently got an important new feature, which allows you to stream TV from your SlingBox over 3G. Previously, it only worked over Wi-Fi.
iCarly - Sam's Remote
This one is for the kids: Fans of the cable TV show "iCarly" may appreciate the $2.49 "Sam's Remote" app, which includes sounds from the show.
A $3.99 app called PhotoKeys:Photoshop Remote puts the Adobe Photoshop toolbar on your iPhone. Not for everyone, but could be helpful for some setups.
Apple's free Remote software also controls the Apple TV set-top box, if you have one of those.
A recent update adds a nifty feature that lets you use your iPhone's multi-touch screen as a "gesture pad" to scoot around the Apple TV display. This is much easier than using the small, plastic remote that came with Apple TV.
You can also use the Boxee remote app to remote-control Boxee, if you've loaded that onto your Apple TV.
Sonos Home Stereo
Pro audio software
X-Plane Flight Simulator
Sort of like how Nintendo's DS has a touch-sensitive second screen that often controls what's happening on the first screen, this will let you control and observe some of your flight simulator's features - on your computer - using the iPhone as a smaller, second screen.
Ladies: We're not quite sure how this one works, but the $12.99 "Boyfriend remote" app is worth every penny if it performs magic.
You can tell it to "give me money", "forget about beer" and even "take me to the mall". Classy.
(What's Boxee? Think of it as a multimedia-specialised Web browser that you're supposed to steer from your couch.)
VLC Media Player
Plenty of security camera monitoring apps in the App Store, depending on your rig.
By far the most expensive, though, is Lextech Global Services' $999.99 iRa Pro, which delivers "a video command centre to the palm of your hand".
Digital SLR Camera
If you hook your Canon EOS or Nikon DSLR camera up to a computer via USB, you can remotely control settings, fire the shutter release, and see your camera's viewfinder remotely over Wi-Fi.
The main drawback is that your camera has to be hooked up to a computer.