I like the following apps, all of which are free, except one:
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Quicksettings (by Sergej Shafarenka): includes WiFi Hotspot, flashlight, quick settings.
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PowerAmp ($4.99, but free to try for 2 weeks): Has equalizer. Can boost sytem volume. Only music player that plays all WMA files and can read all WMA artist tags.
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Ulysse Gizmos: Compass, GPS stats, bubble level, & speedometer.
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MyPhoneExplorer: Let's you sync Microsoft Outlook contacts, calendar, and other folders (like music, photos, etc.) between your PC & phone, and manage your phone's files & folders from a PC over WiFi or USB. (You also must download a free PC app.)
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Google Goggles: Not only scans bar codes, but also QR codes &
actual physical objects! (E.g. Take a picture of a coffee machine and it may recognize the exact model based on the image, and then facilitate getting information about it for shopping. Freaking amazing.)
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Lookout Mobile Security: Antivirus and lost-phone finder. Let's you log into a website and remotely ring (siren) your lost/stolen phone at full volume or remotely turn on the GPS and track its location.
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Ultimate Stopwatch. Stopwatch. Countdown timer. Multiple lap times.
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Android Speedometer: Gives max & avg. speed, etc, so fun for skiing, biking, etc. Optionally can display speedometer mirrored onto windshield for driving (i.e. HUD, heads up display).
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Overdrive: For downloading/playing audio books & music from your local library.
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RockPlayer: Plays most video & audio formats-- including SD-based FLVs, MP4, MPG, AVI, WMV.
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Where's My Droid: Let's you locate a lost phone by sending it a secret text message which turns up the volume to maximum and makes it ring, or a text message which makes it text you back a google maps link with its GPS coordinates (which can be amazingly accurate-- like getting you within a few feet of your lost phone if it can see multiple GPS satellites.)
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TiKL: Turns your phone into a walkie-talkie if your friends also have TiKL. Great for skiing, biking, hiking, etc, where you want to insantly talk to one or many with a button-push, not dial & wait for for them to pick up.
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Scanner Radio: Let's you listen to any of hundreds of local police/emergency scanners around the country. Useful if you're stuck in traffic wondering if it's an accident or there's a local emergency, or something.
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QR Droid: Let's you make your own QR codes, which you can then use to easily give people your contact information. You call up the QR image and they scan your screen with their phone's scanner.
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Sipdroid + Google Voice App + Google Voice Account: Let's you do free, Internet (VOIP) based phone calls to anywhere in the US, and receive them on your Google Voice phone number from anywhere worldwide as long as you have an Internet connection (e.g. via WiFi). A bit complicated but detailed setup instructions
here.
Built-in apps: Voice Search, Navigation, SprintTV, and Lattitude (if you want to keep track of where your kids are).
Oh... and I find the phone functionality pretty useful too. You can actually use these Android devices to make and receive phone calls!
