Well, if we're only talking about the collapse phase rather than the events that led to it, comparison to controlled demolition or collapse due to seismicity isn't totally inappropriate. In a standard demolition, the vast majority of destructive energy is from gravity, with the demolitions themselves merely serving to release it all at once.
There is a bit of a scaling problem, however, since the gravitational energy of a structure scales roughly as the square of its height -- GPE = m g h, and both m and h increase at least linearly -- so, viewed in terms of GPE per floor area, the WTC Towers were about twenty times higher than any controlled demolition ever. Similarly, earthquakes have only dropped structures up to about 20 floors high as far as I know, so again the sheer amount of energy per area is much higher.
Others have drawn parallels to avalanches, either of snow or other debris -- Dr. Benson (of the Bazant, Le, Greening, and Benson paper) had an exchange here with myself and others, and we concluded that analytically the speed of collapse is comparable to these phenomena. An avalanche of 300,000 tons of material, over a distance of 300 meters vertical, is not too incredible to imagine.
By sheer energetics, the destruction could be compared to naval disasters such as the sinking of IJN Yamato -- the vessel in question displaced roughly 70,000 to 75,000 tons, and fires caused by repeated attacks eventually triggered her aft main magazine, detonating perhaps 20-50 tons of TNT and destroying the vessel in short order. This compares to a mass of 300,000 tons and gravitational energy of about 100 tons TNT equivalent for each tower. Naturally, the construction, containment within the water, explosives vs. gravity and so on are all quite different, so you should not read too much into this comparison.
