S3 Ep1 & Ep 2 spoilers
Merlin's keep Posted a few spoilers from S3E1 & S3E2.
It appears that they have seen more promotional pictures which I think will come out soon.
Anyway, Instead of making new posts I may add new stuff here unless major promotional stuff comes out.
New Spoilers Added on 8/25/10:
The first episode features a character that is described as Arthur's illusion of a sodden boy.
Morgause will accompany Cenred and his army on, at least, their journey to Camelot.
Sir Leon will be in the first episode. If he will be in the second episode, which is the conclusion of the premiere, is currently unknown.
Merlin gets to fight alongside Arthur, using a sword, in the second episode.
Costumes in the first episode include Morgana's lighter green dress, Sir Leon's casual armor from The Nightmare Begins and Arthur's traveling clothes from The Last Dragonlord. Although it's hard to tell based on the quality of the source, it looks like Gaius will be wearing his brown robe from the first season in some scenes.