Recommended Green Lantern:
-Green Lantern: Emerald Dawn - The modern origin of Hal Jordan, the main Green Lantern.
-Green Lantern: Emerald Twilight - The downfall of Hal Jordan and his rise to power as the evil Parallax. The GL Corps and Guardians of the Universe are Destroyed, Kilowog dies, Sinestro dies, Kyle Rayner recieves the last GL Ring in the Universe.
-Green Lantern: Rebirth - Hal Jordan's return as a Green Lantern and his struggle to free himself of Parallax and Spectre. Sinestro also makes an appearance and all the GLs have a time in the spotlight.
-Green Lantern: Sinestro Corps War - The most action pack and well executed "event" I have ever read. If this doesn't get you're heart pumping, then you don't have a pulse.
Recommended Grant Morrison:
-JLA: New World Order - The opening storyarc on Morrison's legendary run of JLA. The White Martians invade Earth but are received as heroes by the populace and it's up to the JLA to stop them.
-JLA: Rock of Ages - This is the ultimate JLA story, IMO. It has an epic story, grand villains, Darkseid, and an alternate reality.
-JLA: Crisis Times Five - Morrison's JLA teams up with the newly reformed JSA in one of the greatest crossovers between the two teams.
-New X-Men: Planet X - The most "realistic" take on the X-Men I have ever read. Magneto successfully infiltrates the X-Men team as a mutant known as Xion.
-X-Men: Here Comes Tomorrow - Awesome alternate universe story in the tradition of Age of Apocalypse.