I would say the Crystal Wars in Asheron's Call. They made everyone decide if they wanted to defend or destroy the crystal and 1 server (out of 8) actually defended it night and day for the entire event (about a month) then the devs pulled some story characters out and called for the help of one of the only people with the dark shard (basically someone who swore allegiance to the enemy for power) to help destroy the crystal. There is a video of it I saw a while ago but AC is always overlooked because it only had about 13,000 subscribers at its peak. Everyone I know through out my MMO careers who have played AC agree in it's prime it was the most engaging MMO to date. It had a ongoing story...Things could change every month. I'm disapointed in all the MMO sites that don't acknowledge it. Just because you missed it doesn't mean it didn't exist. No offense intended.