1. The Colossi, Shadow of the Colossus (PS2, 2005)
SOTC could well have been designed as the result of a late-night "What's the biggest boss you've ever seen?" discussion - there are no minor enemies, just bosses. And those bosses are moving, breathing levels.
Each has to be climbed to be killed - and the fact that this can take up to half-an-hour should give you some indication of the scale we're talking.
Above: So big, you'd need to turn a widescreen TV on its side to actually get a shot like this.
If you haven't played it, anything we can mention or show will only spoil the effect; but if you want to feel like a true giant-killer (and, weirdly, it's not as good a feeling as you might think) no other game comes close to doing it like this.