Toyota 4A twincam. Just cos you can thrash the begeezus out of them everyday, and generally all they require is fresh oil + filters. (lambo/ferrari type engines are hi-performance, but the servicing UGH)
For those who are wondering, it's a mighty 425cc flat 2 from a Citroen 2CV. Note that it's *not* a boxer, so that when you stop at lights, the whole car shakes from side to side as the pistons move