If you want the only (99%) F2P MMo with tons of content for both solo and group then there is only AION. The combat and PvP is second to none and there is NO GRIND! plus you can level to cap without having to purchase any expansions as you get everything as standard. Server populations are nearly always full across the board.
Another shout for Aion from me.
It has an excellent art style and the combat chain system is very nice.
As eekfek has said, there is barely anything you have to grind when levelling but do bare in mind that there are some limitations to the f2p crowd. The most annoying of them is no use of the player market system and no posting on looking for group board. However not having access to the broker isn't a gamebreaker as you can get decent armours and weapons through quests which give you coins.
@eekfek: What server you on?