Racing engines have wilder or more pointy cam profiles, enabling the valves to open sooner and stay open longer.  They produce a prodigious amount of power at high revs.  However, they're somewhat limp at lower revs, and snarl and pop at idle. Until recently, road car engine designers have had to compromise and set their cam profile somewhere between the two extremes.  So we’d get engines with average torque, average fuel efficiency, and average performance. 

Enter Honda.  In the 1980s Honda came out with the first application of variable valve timing in a road car.  Instead of one cam profile, the Honda Variable Valve Timing and Lift-Electronic Control (VTEC) engine contained two settings, one for low rpm and one for high rpm.  At low rpm, the cam profile was mild, and at a certain changeover point, the more aggressive cam profile would take over.  So at a certain rpm, your previously docile Civic would transform into a wild animal. 

Honda engines with VTEC have improved both fuel economy (about 8% better than non-VTEC counterpart) and high-end power.   VTEC-E is actually the Economy VTEC used in lower-end Civics, used primarily to improve emissions and fuel economy.  DOHC VTECs are tuned for high-end power in the Civic SiR, the Civic, Accord and Integra Type-Rs and the S2000: not much happens below 6000 rpm, but rev it past that point and you awaken the monster!  You can rev to 9000 rpm, too!

Here's an illustration of Honda's new 3-stage VTEC, already in Japanese Civics:

In stage one, for low revs, the engine uses two different cams for the two intake valves.  The cam on the left, the nearly round one, just cracks open the left intake valve, while the right cam, with a medium profile, operates the right valve with medium lift.  With the left valve just barely opening, the fuel-air mixture is swirled in the cylinder before combustion, resulting in good torque and low emissions.

Stage 2 is for medium revs.  Oil, illustrated as orange, is pumped into a cylinder, locking the two outer cams together.  Now both valves are made to follow the right cam, for medium timing and medium lift.  

At high revs, Stage 3, oil enters both chambers of the VTEC system, thus locking all three pins together.  Now both cams are forced to follow the middle cam, which has quick timing and high lift.  This generates the top-end power that Honda VTECs are famous for.

Honda was the first to come out with a market application for variable valve technology. Now popularly known as VTEC, Honda's know-how can be felt in much of its line-up from the mundane City Type-Z to the phenomenal Acura NSX and S2000.
From a 1.6-liter engine, Honda was able to squeeze 185 bhp in the form of the Civic Type-R. Using DOHC the redline of the Type-R is around 8500 rpm...that's 1000 rpm more than the Civic SiR.
However, the ultimate DOHC VTEC is the one used for the S2000.  Using just a 2.0-liter inline-4 engine, the Honda S2000 has 240 bhp! That's 120 bhp per liter.  Normally, it takes a turbocharger to bring out such performance. However, given a 9000 rpm redline, the S2000's engine is probably one of the most powerful 2-liter normally aspirated unit out there.