Assassin's Creed reference...
	Combining Herbs (Resident Evil...
	Elder Scrolls Reference...
	Skyrim Easter Egg...
	Various Steam Achievements...

Once you have beaten the regular story, revisit Weathertop (doing so after nightfall seems to work best). Use the rope on a hook and a board appears. Proceed to the end of the board and a trail of blue studs will appear that leads to a puddle. If you leap off the board, you'll hear the sound of an eagle and then land in the puddle, like an assassin leaping from a viewpoint and landing in a bale of hay or some brush in the Assassin's Creed games.

As you work your way through The Battle of Pellanor in Free Play mode, you can dig up a Red Herb and Green Herb, which can be combined into a Med Kit that is used to heal an injured soldier.

There's a Fetch-Quest in Edoras (near the Warg Attack mission) where the guy talks about how he used to be a citadel guard, until he took an arrow to the knee.

When you talk to the man over the gates to Rohan, he will ask for bandages, explaining that he "took an arrow to the knee." This line is a reference to the famous line from The Elder Scrolls V: Skyrim.

Achievement	How to unlock
... And away he goes, Precious!	Defeat Gollum as Gollum.
A link to the elements.	Craft the Fire and Ice Bows. (Single Player Only)
A Wizard should know better!	Complete 'Osgiliath'.
An expected journey.	Travel to Trollshaws as Bilbo.
Dance of the dead.	Turn an enemy into a skeleton and make them dance.
Delved too greedily...	Collect more than 10,000,000,000 studs. (Single Player Only)
Don't tell the Elf...	Throw Gimli 30 times.
Great! ...Where are we going?	Form The Fellowship of the Ring.
Here's a pretty thing!	Craft every Mithril item. (Single Player Only)
I told you he was tricksy.	Collect all the Red Bricks. (Single Player Only)
I'm glad to be with you.	Complete a level in co-op.
I've always been taller!	Use the Ent Draught on Pippin.
It won't be that easy!	During 'Prologue', jump into the fires of Mount Doom as Isildur.
It's a dangerous business...	Complete 'The Black Rider'.
It's gone.	Complete 'Mount Doom'.
Let's hunt some Orc!	Complete 'Amon Hen'.
My Precious...	Collect all the Mithril Bricks. (Single Player Only)
Naughty little fly...	Complete 'The Secret Stairs'.
Not with 10,000 men...	Unlock all characters. (Single Player Only)
Of all the inquisitive Hobbits.	Unlock all the Map Stones in Middle-earth. (Single Player Only)
On the Precious...	Complete 'Taming Gollum'.
One does not simply...	Walk into Mordor.
Our only wish to catch a fish!	Fish perfectly 20 times by pressing the icon as it flashes.
Pointy-eared Elvish princeling.	Defeat 42 Uruk-hai as Legolas.
Ready for another adventure.	Achieve True Adventurer in every level. (Single Player Only)
Return of the Mushroom King.	Equip Aragorn with the Mushroom Crown.
Safe is where I'll keep you.	Complete 'Track Hobbits'.
Soft and quick as shadows...	Complete 'The Dead Marshes'.
Stinking creatures...	Complete 'Warg Attack'.
Taking the Hobbits to Isengard.	Travel to Isengard as every playable Hobbit.
That is a rare gift.	Reach the top of Amon Hen without being caught once by Boromir. (Single Player Only)
That is no trinket you carry.	Complete 'Weathertop'.
That one counts as mine!	Finish one of Gimli's opponents as Legolas in 'Helm's Deep'.
That still only counts as one!	Defeat an Oliphaunt as Legolas.
The battle is about to begin...	Complete 'Helm's Deep'.
The long way around.	Complete 'The Pass of Caradhras'.
The Lord of the Ring.	Complete the Bonus Level.
The strength of Men failed.	Complete 'Prologue'.
There and Back Again.	Get 100%. (Single Player Only)
There's some good in this world.	Complete all the Fetch Quests in Middle-earth. (Single Player Only)
They have been summoned.	Complete 'The Paths of the Dead'.
This day we fight!	Complete 'The Black Gate'.
This is no mine... it's a tomb.	Complete 'The Mines of Moria'.
We cannot linger.	Complete 'The Mines of Moria' in under 15 minutes.
We did it, Mr Frodo.	Complete 'Cirith Ungol'.
What about second breakfast?	Complete 2 cooking puzzles.
Worth greater than the Shire.	Dress a character completely in treasure items.
You and whose army?	Complete 'The Battle of Pelennor Fields'.