Key Issues - Cable Volume 1

Cable is one of my all time favorite characters in comics.  Although the X-Men already had Wolverine and Gambit as resident bad asses, they still bought into Xavier's methodology for the most part.  It was interesting to see a hero who believed in the dream but disagreed with Xavier on how to get there.  I'm hoping that because she was raised by Cable, we'll see Hope begin to show lots of Cable's character traits.  I think we're already seeing some of that with Gillen's Generation Hope.  Lots of these issues can be picked up from the $1 bin at your local comic shop.
 

Cable #1:  1st Sinsear, 1st Clan Chosen
Cable #3:  1st Weasel (Jack Hammer).  Both Marvel's Wiki and Wikipedia list his 1st appearance as Deadpool: The Circle Chase #1 however it was August 1993 while Cable #3 was July 1993.
Cable #6 - 8:  "Fathers and Sons" arc.  Cable finally revealed to be Nathan Christopher Summers
Cable #15: 1st Marrow
Cable #24:  Death of Grizzly
Cable #34:  Cable fights an Onslaught controlled Hulk
Cable #40:  1st Abyss (Nightcrawler's half-brother)
Cable #43:  1st work by Brian K. Vaughan (Y: The Last Man, Ex Machina) at Marvel.  He did the dialogue on this issue.
Cable #48:  1st Irene Merryweather
Cable #59:  1st Jack Truman (S.H.I.E.L.D. Agent 18 who later becomes Deathlok)
Cable #64:  Cable origin retold
Cable #87:  Death of Pyro
Cable #88:  1st Dark Mother (Fiona Knoblach)

Cable #97:  Begin Tischman/Kordey run
Cable #100:  Cable frees himself of the techno-organic virus

Cable: Blood and Metal #1 - 2:  These are key issues for Cable's history leading the Six Pack.  If the X-Cutioner's Song crossover were released today these probably would have been considered a limited series prelude.

Crossover Issues:
Phalanx Covenant:  Cable #16
X-Men Legion Quest:  Cable #20
Onslaught:  Cable #34 - 36
X-Men Zero Tolerance:  Cable #45 - 47
Apocalypse The Twelve:  Cable #75 - 76
X-Men Ages of Apocalypse:  Cable #77
X-Men Dreams End:  Cable #87