My first comics were Spider-Man and X-Force against Juggernaut, when Juggernaut singlehandedly toppled one of the World Trade Center buildings, followed by Spidey "dying" long enough to see the other side and fight Thanos one on one and wake up just in time to fight the Sinister Six. Great string of comics there. Oh, and X-Men 1-3, with Magneto and his Acolytes.
If nobody's mentioned Alan Moore's "Watchmen", I'm in deep shock. Truly one of the finest comics I've read. I tried to anjoy Art Spigelman's "Maus", but that's really depressing shit.
House of M was good, in my opinion. The core title was, at least. Real tense, made me feel like a war was coming, and when it hit...it petered out. Whatever, though. Cyclops leading everybody gets my vote for stroke of genius. Civil War is great, but I keep overlooking Frontline and there's just no way I could give a shit about Infinite Crisis...that's the most convoluted mess I ever tried to read.