Adventure Quest > Runescape. Unlike Runescape, AQ is good for coffee breaks.
I'd have to reccomend Allegiance (www.freeallegiance.org) to all of you.
Reason number 1:Space combat!
Reason number 2: Full 3D Graphics!
Reason number 3:Great community
Note: These are in game screenshots, or at least using in-game art and such.
It requires downloading and an email account, but you obviously have such if you've got a Grounds gold account.
Note 2: There are a lot of useful resources for learning the game, such as Allegiance Academy , and the site's knowledge base, so please see if your questions are answered there(especially the basics of how to play) before attempting to ask experienced players.
Note 3: Your IQ must be at least 90 to play, or you will be ostracized by the community.