My short take on all the mentioned by HESKEY (like I said, I played them all :p):
Miwiw99 recommends 'Silkroad Online R' if you love the grinding experience, and also 'Lord of the Rings Online' for casual play if free.
Silkroad Online is like Miwiw said, it's an AZN grinder botfest, I don't know much about it beyond that, but that alone is enough to put a huge NO stamp on it. LoTRO is nothing special, typical generic PvE MMO and I would only play if you're crazy about the LoTR lore.
Myself and Gravoth_iii vouch for 'The Old Republic' for fun questing and dialogue options ingame in the Star Wars universe.
The Old Republic is a decent SINGLEPLAYER game. I had fun leveling and completing the story but after that, the endgame just sucked. I did stick with it for a while after I hit the level cap but it got really boring really fast. Standard grind PvE and PvP instances for gear endgame. Very very little open PvP.
Pollux says 'Age of Wushu' for martial arts and PvP stuff.
This is one of the few that I actually would recommend right now. For the time I played I had fun with it. Didn't stick with it because I didn't have the time to play MMOs. There's a lot of different stuff and interesting features it has, and also some minigames to make the tedious chores a bit more pleasant. You also have some of the generic mmo stuff in it that might bore you. It's PvP heavy and kind of like EVE. While it is free there are some advantages to being a VIP user (15$ per 2 months I believe). Avoid if you dislike AZN / martial arts theme. (if you recall, I made a thread about this game a few months ago
http://forum.melee.org/and-all-the-other-things-floating-around-out-there/age-of-wushu/msg689240/#msg689240)
Clockworkkiller says 'Fallen Earth' for the faction system and open world PvP in post apocalyptic surrounds.
Fallen Earth... dunno really. It seems like the idea is good but the game was just meh. It just got boring very fast.
Finuad likes what he's seen of 'Neverwinter' so far (but it's got a lot of flak from others here).
Neverwinter is meh at best. It's like World of Warcraft really. It has that dungeon maker feature and a bit more actiony combat, but there's nothing beyond that.
Kafein says 'PlanetSide 2' cos apparently the game keeps changing.
Planetside 2 you know about already.
Polobow says 'Mabinogi' is a love-it or hate-it game.
Been years since I played this. It has a few unique features but very outdated cell-shaded graphics. I can't recall how much of a grind it was. Also AZN/chibi themed, so you mind find that annoying.
CrazyCracka says 'Ultima Online' and goes into good detail about it's features (too much to list here).
Ahhh UO. Ultima Online can be great if you can get past the outdated graphics, controls, UI and combat system. It has some really neat features that other MMOs should really learn to adopt. It was great for it's time.
Benkei says 'Lineage 2' for a skill-based 'Asian grinder' with awesome PvP.
Lineage 2 has very interesting PvP. Castle sieges, land control, control land control taxes in villages, etc. The main problem here is the grind. And there's a whole lot of fucking grind. Also not that interesting tab target combat.