I have always been a firm believer in using a metronome at all times when you are practicing. These days it's now easier than ever with good metronome apps available for your iPhone or Android phone so you can bring it wherever you go--so there's no excuse for bad time! ProMetronome for iPhone recently updated their application and now it is better than ever.
ProMetronome is currently my top choice for using a metronome both for my own practicing and lessons with students. The colors are bright and it's easy to distinguish the different beats and follow along with the time. In addition, the interface is very user friendly, making the app very easy to use for students of all ages. I haven't upgraded to the "pro" version yet, so if you want to use the app is landscape mode you will need to do that. Most importantly, there are a wide variety of metronome click sounds to choose from and they are very loud! My biggest complaint with other metronomes is the sounds not being loud enough to hear over instruments.
For Android phones, I have only used one app consistently that I like--Mobile Metronome. This app is free and has a nice user interface. As with ProMetronome, the metronome clicks are also loud enough for a multitude of musical environments. As with most apps, if you want to get rid of the advertisements at the bottom you must upgrade. If using an application on your phone won't work for you there are other good options like traditional metronomes.
I grew up using metronomes, and often times having a separate metronome to keep in your instrument case or backpack (especially with children) is the best option. In this case, I would recommend the Korg TM-40 Large Display Digital Tuner and Metronome. This rugged metronome also features a tuner so not only can you keep time, but you can stay in tune! The display is easy to read and the buttons are straight-forward and basic to understand. There are many great metronomes out there, from more compact credit card sized ones to larger metronomes with more controls and sound options, but the Korg is great for students because it has everything you need and will withstand many drops to the ground.
Thanks for reading! Please contact me with any questions or comments.