If you're looking for songs to practice to, country or rock, you can download "danceables" on your iPhone or Android phone. It has a list of over 10,000 songs and the dance associated with it. It's pretty cool.
When looking for ballroom dance music it is important for it to be played at the right Tempo. To find out what is the right Tempo for each of the dances simply go to Wikipedia List of Dancesport Dances. It is as simple as that.