I haven't really ventured off of my few main games over the years.
My first MMO was Star Wars Galaxies from launch until they messed that game up. Will always have a soft spot for a lot of things they had in that game. I've been playing LOTRO since launch with plenty of breaks in between. I also tried out SWTOR but just can't get into it for some reason.
These days I really don't have a lot of time to sink into an MMO as its so time consuming. I get a lot more enjoyment out of the NHL games and FIFA games for the most part.
I can't even describe with words how much I miss the original SWG.
There's actually still illegal emulated servers around (Pre-CU). Just need a copy of the game.