Musically speaking, there isn't too much point in digging too low since our pitch perception really goes down the drain in very low frequencies. A little bit below 20 hz, and we totally lose it, it is just 'stuff' that is being sensed, and it becomes indistinct sound pressure.
For this thread I am only posting the tunes that I like which will give your subs a workout. There are plenty of tunes I could post that are a lot harder on the subs than these, but I just don't enjoy those songs as much, a lot of them are gimmicky 'bass' songs. For example, here is a very brutal tune with tons of energy in deep bass. In fact, it sound like a 'quiet' recording, because the track's dynamic range is almost all eaten up by sub 20 Hz output, and not much is left for higher frequencies. It's not really that bad of a tune itself, but it represents a genre whose purpose is only to pound out low frequency sine waves.
You can see most of the energy is between 25 and 11 Hz. Probably not a great idea to play this at max volume with a ported subwoofer. Most sound systems wouldn't even be able to play about 85% of this tune's content!