Nothing pre 1998 over here,just got back into comics a good 2.5 years ago and finally settled on a stable pull list about last summer so the floppies are fairly recent...
Most treasured floppies would have to be:
from the top of my head...Ultimates 1 and 2,the entire Bendis/Maleev DD run,Wolverine EOTS,Millar's Ultimate F4,Young Avengers,Pak's Hulk,Stern and Buscema's Avengers (Under Siege,Assault on Olympus),JLA Year One,All Star Superman,Johns' current Green Lantern,Justice
Trades and HCs:
Absolute New Frontier,The Golden Age,Planetary 1-3,Authority 1-2,The American Way,Batman Year One,Archer's Quest,Hawkman 1-3,Red Son,Secret Identity,For All Seasons,Birthright,Top 10 1-2,JSA:The Liberty Files,Identity Crisis,Astro City 1