There are many different bands that put out music that will test the limits of your sound system. Each one will test a wide variety of ranges, pitches, and frequencies. It just takes some searching to find some bands that work well. Well since I'm writing the node, I'll give you some specific places to look.

I was working in a new theater and was testing out its new sound system. It consists of 2 "18 subs with 800 watts of power to each. Then 2 rears, to forwards, a center channel, and smaller speakers scattered around. All of this is cranked through a Peavey Media Matrix, and can produce optimal levels. Let me tell you my results from this, and other bands/people that put out good stuff.

DJ Shadow-Preemptive Strike (Track 3) Oh man oh man. This track will put your sub to the limit.

Air-Moon Safari (Sexy Boy) This is an exceptional track to test your speaker's limits. It goes from deep poweful lows to high notes to test those tweeters. Make sure that things are cranked. I tested this one in the theater, and it ran extremely well.

Chemical Brothers-Brothers Gonna Work It Out (Entire CD) This cd is absolutely perfect for testing out sound systems. It fluctuates from all frequencies and pitches, and will push even the most advanced system to the test.

Good Luck! And be careful! Make sure your speaker wattage to amp wattage ratio is greater than 1, or you're screwed.