I guess my Fav is rare.
Dungeons & Dragons Online.
There are quite a bit of bugs, but the UI & graphics PWN Runescape to the extreme! The game works very similar to Runescape, but its definitly less boring. Unfortunately, the game is only available on Windows XP (last time I heard, Windows 7 was still in testing, although I believe some ppl have gotten it to work).
Runescape should surely have a spot here. I am not sure if you can consider it a MMORPG but I love Path of Exile too. I believe you can also play ESO, FF14, and Guild Wars 2 for free, but out of the three, the "free" portion of the game in Elder Scrolls is surely will be the most enjoyable