I realize this is Dark Reign, but reading various posts of people mentioning other storyline got me nostalgic thinking about some of the great story lines I’ve read and would love to see represented somehow. Break out your nostalgia and post some of your favorite story lines please.
In no particular order
Siege of Darkness
Midnight Massacre
Maximum Carnage
Infinity Gauntlet
Infinity War
I really enjoyed the Marvel Civil War stories.
Civil War was great, but the ending was kind of wimpy. I like the classics like Dark Phoenix and Inferno.
Frankie Raye becomes Galactus’ herald
Rebirth of Elektra
Days of Future Past
ps. I’m old
Anything with Deadpool. I am a fan of the merc with a mouth. Deadpool killustrated, Deadpool kills the Marvel Universe, and Deadpool kills Deadpool are my favorites. Basically, I like Deadpool killing things.
You should also read Deadpool: Suicide Kings. The early Daniel Way run was also mostly excellent and some arcs of Deadpool NOW have been awesome.
Infinty * crossovers were pretty good. Definitely Age of Apocalypse as one of the best!
How about Acts of Vengeance? 
It was silly in retrospect, but it got me started buying all the Marvel books!
Maximum Carnage
Secret Wars
The entire run of Thunderstrike (kudos to anyone else who read it)
Joe Kelly’s Deadpool run. All of it, but especially his encounter with Bullseye and his fight against Captain America.
Avengers Forever.
New Warriors vol1, #1-25
My top favorite is Thanos Quest/Infinity Gauntlet, I consider that one storyline, it well written and the art was excellent for that time.
Am more into space operas than earth based storylines, other stories I loved:
Older stuff:
Jim Starlin
Thanos Quest
Infinity Gauntlet, Infinity War, Infinity Crusade, Infinity Abyss
Thanos 1-12
Warlock and the Infinity Watch
even read some his 1970s Warlock comics
Dan Abnett and Andy Lanning
Guardians of the Galaxy 1-25
Thanos Imperative
Annihilation Wave
Annihilation Conquest
Hypernaturals (not Marvel)
Walter Simonson
Thor run
Dan Jurgens
Death of Odin
Currently reading:
Jonathan Hickman
Fantastic Four run
Infinity
Avengers
New Avengers
Jason Aaron
Thor
The “Elf with a gun” saga.
Kieron Gillen on Journey into Mystery (Loki) + Matt Fraction on Thor
Kieron Gillen and Jamie McKelvie on Young Avengers
Jonathan Hickman on Fantastic Four/FF
The Abnett & Lanning cosmic stuff, especially the Nova and Star-Lord/GotG stuff.
classic Doctor Strange
The first Iron Man “Armor Wars” storyline
Nextwave
Matt Fraction and David Aja on Hawkeye
DoFP, Armor Wars, and the Secret Wars serieseseses were definitely good too!
Not strictly Marvel universe, but anyone else love Hama’s Nth Man limited series?
As someone said, Civil War was great even if the ended was kind of a whimper rather than a bang… Though admittedly a deep, fully-realized whimper that brought one of Marvel’s strongest willed characters to his knees in complete failure.
I’ve always always loved the Armor Wars series, and what I’ve read of Secret Wars. Days of Future Past, Deadpool: Suicide Kings (as well as most of Joe Kelly’s, which I’m sure someone has said), most of the Carnage series as well as Punisher AUs… I actually enjoyed Marvel Zombies (I didn’t have high expectations though). Also, in no particular order:
Anything of the Runaways
X-Men Legacy: Fables of Reconstruction (the Omega Sentinel arc with Hellion/Hope towards the end)
The entire Predator X arc
Most of the Nightstalkers
Going to stop here 
Walt Simonson’s runs on Thor and X-Factor. Beta-Ray Bill & Archangel!
Infinity Gauntlet
The Armor Wars
You’re not read Bendis’ Guardians Of The Galaxy, I’m really liking that one.
And I’ll second Jason Aaron on Thor God Of Thunder…it’s just awesome.
True Deadpool fan should never miss Joe Kelly’s run.
Days of Future Past
Asgardian Wars
Age of Apocalypse
Ultimates storyline
Inferno
Secret Wars
Fear Itself
Mostly old storylines since I’ve stopped collecting comics due to their price. Only started reading again when Comixology has sales for digital comics, which I really recommend for everyone. 
What’s a good way to catch up on all these story lines? I really enjoy reading the newer stuff (Astonishing X-Men) but have no idea how to get my hands on the older storylines.
I was never really a big fan of massive crossover events. I found them tiring, frankly. I own Maximum Carnage as a TPB and I never want to sludge through that. Sal B’s artwork is a little…well, I’m sure he’s a nice guy. Oy, and it was so long.
I was also a huge X-Men fan back in the day, so I like the X-Cutioner’s song arc. My favorite is probably Age of Apocalypse, but if you thought we were getting bizarre characters now, just wait for an AoA influx. Don’t literally wait, because it wouldn’t happen, just using a turn of phrase.
I prefer the Phoenix saga over the Dark Phoenix saga, insofar as I was never a big fan of X-Men in space. I think the original had the Hellfire Club, which had some very classic moments.