As a Honda guy (and S2000 owner) the F20C/F22C gotta be in the hall of fame. A production, naturally-aspirated 2.0L four cylinder making 240HP and revving to 9K RPM in 1999 is bonkers! It set the world record for HP per liter from an NA engine at the time, and it took Ferrari to beat that record 10 YEARS LATER with the 458 Italia. And on top of all that, they're bulletproof and can make massive power with stock internals and boost. What a marvel of engineering!
Oh yeah, K20 and K24 obviously belong on that list too :P