For me, nothing can top a well-recorded organ CD. In this regard, the best I've ever heard is one that was passed around a few years ago but never was commercially available. It simply has the most perfect low bass I've ever heard.
Check some of these out:
From a website devoted to the now-defunct Atlantic City Convention Hall organ, which had real 64 foot pipes that did an honest 8hz (and could fake 128 foot resultant pipes and 4hz!), there's this little diddy. After about 11hz, I no longer felt the pressure waves, and only heard the air compressors and reeds flapping back and forth:
Non-organ music goes deep, too. Anyone ever heard of bassist Yves Carbonne? He has a 12-string electric bass tuned down to 15.4hz. AND, he has free MP3s of it on his website. It's definitely an odd sensation hearing an electric string bass go so low -- according to a spectrumlab analysis, 20hz is the lowest he goes on the free MP3s.
Anyway, it's a fun test for your subs. Go here:Yves Carbonne Official Web site
Download them all if you wish, but the two that plumb the depths are "Cherokee" and "Sub_bass_impro_3."
Clapton's "Unplugged" has some low frequency stuff mostly from the mics recording foot tapping on the raised wooden stage:
Here's "Before You Accuse Me," with energy bleeding into the high-20s
The low frequency of a venue in live recordings is easy to pick out. This is "Sleepwalk" by Hank Marvin from the Strat Pack DVD:
And here's "No Quarter" from Zeppelin's 02 gig. Check out the synth bass at 32hz.
"Hotel California" from the Eagles' "Hell Freezes Over" has a nice kickdrum centered at 28hz:
Finally, no low bass list is complete without "Bass I Love You." Strong down to 5HZ!
Download it here: Realm of Excursion
and click on "downloads."