• Prince Imrahil & Keen-Eyed Took 

That must be Sneak Attack + Gandalf (Core).  It is from day one.

To gain Sentinel or help in combat when a shadow card comes up that you can't otherwise deal with… (2+ player games)

Sneak Attack + Landroval
Sneak Attack + Gandalf (core) [destroy the attacker]
Sneak Attack + Landroval + Brok Ironfist


Bofur (spirit) + Prince Imrahil
Errand Rider + Elrond


We Are Not Idle + Lure of Moria [probably one of the easiest and potentially one of the best with 5+ Dwarves]
 

Hmm, with one I forgot, we got 4 common combos, surely there are more?

• Imladris Stargazer + Zigil Miner
• Sneak Attack + Gandalf (Core)/Landroval/Brok Ironfist
• Prince Imrahil +Keen-Eyed Took/Bofur (spirit)
• We Are Not Idle + Lure of Moria

Born Aloft + Gandalf/ Descendant of Thorondor/

Legolas + Blade of Gondolin (3 progress tokens)

Glorfindel + Asfaloth + Light of Valinor

Arwen Undomiel + Boromir (core) - sentinel and multi defender

Gildor Inglorion + Zigil Miner

Glóin + Warden of Healing

Gondorian Spearman + Spear of the Citadel

Rivendell Blade + Legolas

Thalin + Gondorian Spearman

Thror's Map + Asfaloth/Northern Tracker

Thalin + [any weapon] + Gondorian Spearman + Spear of the Citadel + Goblin Cleaver

it looks like a five card combo, but it is not hard to pull

Elrond + Warden of Healing

Hama + Feint / Thicket of Spears

Elrond + Vilya + Imladris Stargazer/Gildor Inglorion + expensive stuff

Hama + Feint (not really a combo…)

Trollshaw Scout + Rivendell Blade + Foehammer:  generates cards to fuel his attacks, & he has ranged to attack anyone. Add Hama to recover the Foe Hammers & Hands Upon the Bow to do it out of turn.

Beorn & Fortune or Fate - the only hero you might plan to lose. Horn of Gondor to mitigate the cost …

Denethor and any attachment that allows him to ready (After seeing the encounter deck) to defend.

Weapon Attachments + Foe-Hammer or Goblin-Cleaver = killing enemies or card draw.

Thalin + Expecting Mischief = Useful to soften enemies or kill them at once.

Fili and Kili + A very Good Tale = pay for one brother, get the other and use AvGT to potentially pull 2 more allies ending with 4 allies with only 3 cost of resources.

Expecting Mischief + Goblin-Cleaver = perhaps not very common but i discovered it by accident. EM dealt 2 damage to an Orc Vanguard (from HoN). Later in combat had many enemies and G-C helped deal the remaining 3 damage to kill it.

Gandalf (Core) & A Very Good Tale &  Another Ally & an ally packed deck (20+,25 best) - Gandalf readies in the refresh phase just before he disappears so using him then for AVGT is "free".