Some of my favorites are...
The Mitsubishi 4g37, not a very powerful engine, but hecka reliable and can take a TON of abuse! I had friends with base model 1st gen Eclipse's that thrashed them to death, but the engine still ran strong.
Also, the Mistubishi 4g63... An increadible engine with crazy power potential. As long as there's been an Evo, there's been a 4g63.
The Mazda BPD 1.8L engine... Nice little dohc motor with good power for it's size. I had a '94 Protege with this engine in it. Didn't burn a drop of oil via 5,000 mile oci's. The engine was great, but everything else in the car seemed to be falling apart.
But the engine I like the most right now is the Ford 4.6L V8. My dad has driven his '92 Grand Marquis for 15 years and the motor still runs like a champ. This influenced the purchase of my current car, 99 Vic and the engine seems to be doing very well so far. It's extremely smooth, reliable, and decent on gas. Ford has been confident enough to use it in a variety of their cars and trucks. The most awesome of which is in the new Mustang. I've read about Taxi cab drivers taking this engine to 300,000 or 400,000 miles and beyond w/out rebuild.