Out of respect for Spoiler free people and in an effort to support their decision and make their navigation around the forum safe, this is the one and only thread where spoilers are allowed to be posted and commented on.
Just in case, once an episode has aired in the UK it is no longer considered a spoiler. It is generally a good idea to avoid the forums until it airs in your country if you are spoiler free.
I have reserved the next two posts to keep track of all the spoilers that are posted. I will arrange them by episode so it's easier for everyone to find all the information available without having to skim through all the posts. Bring them on!
Spoilers for Season 2
Tearful Merlin and soulful declarations of devotion despite Arthur giving him the cold shoulder
In one scene where Arthur is dismissing Merlin in favour of Cedric, a new servant trying to make the apart.
There is a Morgana/Gwen hugging scene.
Arthur/Gwen relationship seems to get started with some accidental falling-on-top-of-each-other, awkward conversation, and a touching moment when Arthur thanks Gwen for saving him.
Spoilers for 2x02 The Once and Future Queen: here
Spoilers for 2x03 The Nightmare Begins: here
Spoilers for 2x04 Lancelot and Guinevere: here
Spoilers for 2x07 The Witchfinder: here and here Preview here
Spoilers for 2x08 The Sins of the Father: here, here, here, here and here Arthur meets his mum!
Spoilers for 2x09 The Lady of the Lake: here, here, here and here
Spoilers for 2x10 Sweet Dreams here, here and here Previews here and here
Spoilers for 2x11 The Witch's Quickening here, and here. Previews here, here and here
Spoilers for rest of season 2 (low quality) here (starts around 00:55)
Spoilers for undetermined episodes: (Source)
The Great Dragon is going to be released 2x12
Lancelot and Mordred reappear: 2x04, 2x03 and 2x11
Gwen will kiss Arthur and also Lancelot 2x02 and 2x04
Uther will marry a woman who is secretely a troll 2x05 / 2x06
There'll be a lot of jousting 2x02
A witchfinder will single out Merlin in front of the whole court 2x07
Arthur will attack Uther with a sword and call him a hypocrite 2x08
Arthur will share a scene with his mother 2x08
There is a scene that involves Arthur and Merlin in front of a pretty lake. Arthur (ostensibly angsting about Gwen, who he'd been kissing in the previous shot) yells desparately to Merlin, "Nothing can ever happen between us!" Merlin says back with a pointed look, "You can change that when you're king..." 2x04
They can also be seen in this BBC Merlin Website, just for UK people though: here
Season 2 promos that can be seen by everyone
Trailer 1: here
Trailer 2: here
Trailer 3: here
Trailer 4: here
Merlin and Gwen will be Morgana's main confidantes although their relationships will be tested.
Lancelot will return (2x04), as will Excalibur and Mordred (2x03 and 2x11). (Source)
Edited 2 total times.