Square, created by Twitter co-founder Jack Dorsey, lets you accept credit card payments with your Android smartphone. You'll be sent a special card reader when you sign up for an account. Both the reader and the app are free to use, but Square charges a 2.75% fee from each transaction.
Get your travel organized with TripIt. Once you've set up a free account, you just forward all your travel confirmations -- airline plans, hotel bookings, you name it -- to an email address set up for you at tripit.com. The service reads all your plans and translates them into easy-to-follow itineraries, all of which are available within the Android app.
FlightView's $1 FlightView Flight Tracker is a must-have for any frequent flyer. The app gives you real-time status updates on your flights and can even send you alerts when something changes. A widget lets you keep the info right on your home screen, too.
Consistently named one of the best apps for Android, Edward Kim's $4 Car Locator provides a simple way to save your car's location and navigate back to it later.
RideCharge's free Taxi Magic app helps you find a nearby cab, book a ride, and track your cab's location. It works all throughout the United States.
If your travels take you to a foreign land, Google's free Google Translate app could come in incredibly handy. The program provides instant translations between more than 50 languages and offers voice-based input. Capice?
Business miscellany Marc Stogalitis and Mimi Sun's free Gmote lets you use your Android smartphone as a remote control for your PC-based PowerPoint presentations.
For complex business calculations, try Edward Falk's $5 RpnCalc Financial calculator.