For about $57.00 you can download a program called Mixmeister which I've been using for at least the last five years to blend my music, remove questionable language and create loops. It doesn't take long to learn and it makes your class "seamless". I highly recommend it!
As far as music tastes go...I have a variety of people in my classes (I teach seven classes weekly) and the thing that has always worked for me is to use an eclectic mix of music. I'm always on the lookout for new stuff and when I hear anything that sounds remotely "spinnable" I track it down. Just don't rely on one genre of music per class. I'd want to stick a pencil in my ear if I was subjected to an hour of hip-hop, country or show tunes!
Vertically challenged, but expanding my horizons.