Let's see here...
I've tried Sanctum of Eventide, Impressive World, WolfQuest, and The Endless Forest. I still play The Endless Forest now and then, but I've kinda 'retired' from everything else. I've never played any of the other games on this list.
Has anyone ever tried Planeshift?
It has a really cool in-game universe, and it's kind of like Impressive Title in that you rp while you kill monsters and get items. However, it requires a pretty big commitment (you are expected to know the ins and outs of the in-game universe and lore before you start playing, and it's a LOT to remember), and you are also expected to be a literate rper, and act in-character at all times.
Nevertheless, it's a really cool game if you're a serious fantasy rper.