Here's what I think are the best.
Requires you to buy the game (no subscription except for xbox live):
Phantasy Star Online - A space themed MMO that is a classic done right. You make your character and go on missions (for the combat). From shotguns to daggers to spears to wands, your human, beastman, elf, or MECHMAN can dungeon run in groups and fight huge bosses. Of course there's also more things to do. Solid game.
Allegedly Free:
maplestory - I'm sure you know about this game already. I used to play it back when it had 4 classes and it was incredibly long to level up and the game was 90% "pressing ctrl". Though my brother still plays and from what I've seen its changed a lot for the better.
Dungeon Fighter - don't know much about it but I've seen friends play. Looks cool, its basically a dungeon fighter like double dragon. Also there's PVP.
Allegedly third person shooter:
S4 League - not really an MMO but worth mentioning since you can buy weapons and clothes and you have a regular character. Its a shooting game that has skills you can use along with your 3 weapons. Custom loadout so that means custom classes. Weapons come in guns, melees, magic (lightning connects you and your target so you can heal or drain), and sentries (deployable stationary devices). One thing I should note is that weapons are bought with in-game currency acquired by performing well in rounds (u gotta win). This money is used to rent weapons and clothes, so you may not like it that much. I think you can buy permanent weapons with real-life cash though