obviously, you got to know which position you are applying.
Here is my idea, but remember that many companies appreciate genalist who can handle many tasks, in this case, you might want to show your main strength in your reel with a few other minor skill.
Animator -- good character animation, better to tell some story as it helps to speak the mood and the motivation of your character. I will say 1 mins is good enough. Many people make the story too long and fail to maintain the quality, which is the worst thing to do. David Bokser's "traffic" <
http://www.scad.edu/dept/anim/gallery/clips/bokser.html >is a good example of animation piece. I remember he went to pixar last summer for an intern.
Special fx -- it will be cool if you can show some programming or expression setup. the reel doesn't have to be long. Many of my friends has reel consist of 3 to 4 fx shots and each of them last for less than 10 sec. It's not a bad idea if you can imiate some fx shots in movies and do it in your own way(but no more matrix bullet time pls :>)
model and texure artist : not quite sure about this, but my friend who's working as modeller has a reel something like this: one photorealist human character, one monster stuff, one car and a background layout. It will be cool if you can show your concept drawings and all those research come along with your model.
There are many other positions...but seems not really applicable in Hongkong.