Nothing really too it:
http://en.wikipedia.org/wiki/Tea_eggs
As for what I use, most recipes call for soy sauce, salt, and star anise while the choice of tea can vary most go with black tea that is strong in flavor.
I like to add sugar as well. I don't really think the amount matters too much as the more you use the more flavor the eggs will have and I think you will know if you have too much.
What I used:
2 black tea bags
1 tablespoon salt
2 tablespoons sugar
1/2 cup soy sauce
I couldn't find the star anise in my cupboard though so thats for next time.
First you hardboil them in regular water, some people like to boil them partially until they are almost fully cooked and then you take them out of the water, run them under cool water and when they safe to grab hit the shell with a spoon all over it but don't remove the shell.
Put all the ingredients back into the pot of boiling water, put the eggs back in. Now simmer it on low for 2-3 hours at least. The pic I took was at only 1 hour.
Here is an updated pic after 4-5 hours.
http://farm4.static.flickr.com/3017/2930107303_2757fc936e_b.jpg[/IMG]