all the games by artix entertainment battleon.com dragonfable.com mechquest.com aqworlds.com epicduel.com
Theres Runescape runescape.com
if you don't mind small download theres Earth Eternal eartheternal.com
i dont play it but theres Freerealms.com
these are all browser based (EE and FR require small download to work)
A good website to find browsergames is http://www.freebrowsergamer.com/
For downloaded MMOs- RunesofMagic.com is free but you can buy items ingame with real money wow-europe.com is possible to play free but not going in detail since not very legal... GuildWars.com you have to buy game but thats it
I'd say Runescape, or WoW if you're willing to pay. DON'T play AQworlds. I don't really like it that much and it's kinda directed at 10 year olds, and the quests reset.
Guild wars is personally my favorite, Can't wait for Guild Wars 2. P.S. you have to buy the game but no monthly fees or anything else P.S.S the game costs like 40$ so it's not too expensive P.S.S.S here's a video about GW 2 http://www.guildwars2.com/en/media/videos/