One of the best way to find good ballroom dance track is to see what other people recommend. Dance Forums has a great resource devoted to ballroom and other dance music:

Bolero
Cha Cha
Cumbia
East Coast Swing
Foxtrot
Hustle
Jive
Merengue
Paso Doble
Quickstep
Rumba
Salsa/Mambo
Samba
Tango
Tango Argentino
Two Step
Viennese Waltz
Waltz
West Coast Swing