Ford 302 V8, started as a 221 in 1962 and proved themselves reliable and a decent performer through the mid/late 1990s. The appeal of the Mustang “5.0” liter 302 was so great that Ford is again making a new/different 5.0 engine, the Coyote.

Ford 300/straight 6. This engine was produced from 1965 into the 1990s. They appeared in everything from regular cars to dump trucks to tractors to Baja 1000 trucks.

I was going to say the Chevrolet small-block 350 LT1, but instead decided on the LS2.

I respect the former, but consider the latter to be iconic due to the amount of LS swaps that happen around the world (sometimes instead using other LS variants such as the LS1 or LS3).