When I first began dancing, my dance music library was lacking, as were my skills for finding the beat within a dance-able song. Also, I found that during my practice, the songs would end (as they all do) and I’d have to restart my dance.
During a search to find a beat generator, an app that plays the appropriate beat for a dance style, I came across DanceTime Deluxe, an iPhone app that has exactly what I was looking for, and more. It has 26 different dance rhythms to suit as many styles. It allows you to vary the speed of the rhythm, which can be a very helpful practice assist. Also, it has an optional “instructor” that counts for you.
I use it quite often and recommend it to all my students and dance friends who have iPhones.