Like alot of you i'd love a perpetual MMO of Civ... but there isn't one 
Here's some games I found which are a bit like 'Civ Online'. They are all browser based, free, and require no downloads too!
First off there's Travian
Its been mentioned before on these forums and its worth a look. You control villages across a vast map, its very pretty, and a lot of fun. Warning though its a timesink!
www.travian.com
Ogame
Like travian, far more complicated. In space.
www.ogame.org
Cybernations
Great fun! Theres nothign to do really mind... but its nice for a tea break. It only takes 5 minutes a day. There is no excuse for not playing it.
www.cybernations.net
Then theres Inselkampf
German for 'Island Wars'. Is a cross between Ogame and Travian, although slightly less, pretty. The beauty is in its simplicity and community. There are some graphics, although it looks like a text based at first glance. Instead of planets or villages, you control Islands and capture these islands off of other players.
I prefer it to Ogame, because its geographical, like Travian. Geography is important and a nice map shows these relationships.
I have to admit to preffering it to Travian too. Travain is far prettier, but requires a shocking amount of activity to do well in. Inselkampf has a tremendous community (only just getting started on the .com server), diplomacy and argument are all part of the fun.
www.inselkampf.com
Harldy an unbiased roundup i agree, but try them all, being a Civ player gives you some advantages.

Here's some games I found which are a bit like 'Civ Online'. They are all browser based, free, and require no downloads too!
First off there's Travian
Its been mentioned before on these forums and its worth a look. You control villages across a vast map, its very pretty, and a lot of fun. Warning though its a timesink!
www.travian.com
Ogame
Like travian, far more complicated. In space.
www.ogame.org
Cybernations
Great fun! Theres nothign to do really mind... but its nice for a tea break. It only takes 5 minutes a day. There is no excuse for not playing it.
www.cybernations.net
Then theres Inselkampf
German for 'Island Wars'. Is a cross between Ogame and Travian, although slightly less, pretty. The beauty is in its simplicity and community. There are some graphics, although it looks like a text based at first glance. Instead of planets or villages, you control Islands and capture these islands off of other players.
I prefer it to Ogame, because its geographical, like Travian. Geography is important and a nice map shows these relationships.
I have to admit to preffering it to Travian too. Travain is far prettier, but requires a shocking amount of activity to do well in. Inselkampf has a tremendous community (only just getting started on the .com server), diplomacy and argument are all part of the fun.
www.inselkampf.com
Harldy an unbiased roundup i agree, but try them all, being a Civ player gives you some advantages.