Heres a list of skirmishes available at SOM release (some require an unlock)
Trouble in Tuckborough (30-65)
Brigands and goblins have laid siege to the Great Smials. You have to clear their camps and confront their leader to free the Thain.
Siege of Gondamon (30-65)
Gondamon has been under siege by the Dourhands and Blue Crag goblins for nearly two weeks. It's up to you, Mathi, and the Gondamon NPCs to endure the lengthy waves and bring down their leader.
Stand at Amon Sul (35-65)
Help Candaith hold the summit of Weathertop from the forces of a ravaging Cargul, keeping campfires lit in the pouring rain to hold the dark at bay.
Survival: Barrow-Downs (40-70)
Make a stand at the Dead Spire against ever more powerful waves of undead horrors. You'll be overwhelmed eventually, but how long can you hold out before that?
Thievery and Mischief (45-65)
Brigands have seized the south of Bree! Bring justice to their ranks, fight from the Auction Hall to the Town Hall to clear them out of town.
Defence of the Prancing Pony (50-65)
Brigands are attacking Bree, causing the citizens to hole up inside the Prancing Pony. Drive off the attacking brigands, and prevent them from burning down the Pony.
Ford of Bruinen (55-65)
Orcs and Uruks are driving siege engines toward Rivendell! Make your stand against them with Elrohir and Elladan on the Ford of Bruinen.
And the Epic-gated ones:
Strike Against Dannenglor (60-70)
Assault the morroval-infested ruins of Dannenglor and rescue prisoners from it.
Protectors of Thangulhad (60-70)
What was once a key fortress of the orcs is now held by a small band of elves. Unfortunately, the orcs are marching there in force. Fortunately, the ballistae and catapults still work...
Breaching the Necromancer's Gate (65-70)
An assault on Dol Guldur
Assault on the Ringwraith's Lair (65-70)
Continued from the Necromancer's Gate
Battle in the Tower (65-70)
The conclusion of Book Nine: Fortress of the Nazgul