Being rather poor right now i've been playingKnight Online
and Anarchy Online
. Both offer free accounts and no fee download of the game itself and can be pretty fun, especially if used just to break off the monotany of your paid game.
Knight Online is more developed for large scale PVP battles but unfortunately unless you have obtained level 60 + (70 being the max) your not likely to fair very well. The major downside to me for this game is there are no European servers so the community is extremely multi-lingual, and in game communications can be very difficult if you dont speak turkish (they seem to be the majority). Also there is very limited character classes, Rouge Archer/Assassin/Warrior/Mage/Priest and little room for character customisation. There is also the small problem of the shortage of hunting grounds when can at certain times of the day pose a real pain in the rear, however despite all these setbacks it was a pretty fun game to play completely free.
Anarchy Online is a great break from the traditional Fantasy line of mmorpgs and offers a sci-fi based world. There is never an issue with finding a place to go and slaughter monsters, lots of different skills/classes/jobs to chose from, and has a really great in game society including highly active GMs who are often visible at any in game events. I pick this one mainly for the great street parties that can often be found where large groups of players can be found partying it up in the streets while all streaming music from the live DJ dancing it up beside you and taking requests. If your looking for an mmorpg with a nice laid back friendly environment give this game a check. It also offers additional areas and items to paid accounts (expansion packs only available to subscribers), but there is still plenty to do on a free account.
I know this isn't quite in line with the topic as the "best" mmorpgs out there, but if your like me and don't have the spair cash to go buy the newest games out, or just need a break from your everyday game and want some no cost fun, both these games are a great solution.