NCSoft are working on a number of free to play MMOs where you have the option to pay for items / extra content.
Dungeon Runners sounds the most interesting of them - and Open Beta is apparently coming soon - check it out at
www.dungeonrunners.com
Its a MMORPG that looks a bit like a cross between Diablo 2 (potions / town portals / combat) but with World of Warcraft style graphics and quests.
