GW2 perhaps?
Runescape
FFXIV (Especially since there is so much more to do other than combat)
The Old RepublicPart combat, part flying a ship around and making stuff explode in (optional) rail shooting segments, and a whole lot of story. Side quests are optional and kinda blend in with the killing you'll be doing in the first place. Quite early on, and I don't know what the end-game is, or whether or not it's been changed. Monthly subscription.