Todd Dangit

I've gone through a lot of apps for vocal training and general practice tools. This is the best one. A close second is Pro Vocals, which looks nicer but you have to pay for most of the workouts. They do have some killer breath ones though. This one just comes loaded with a ton of goodies. You can customize a routine, or have it do one randomly for you. It's simple to use and follow along with. If you can only afford one vocal app, it should be this one.