A few weeks ago, I discovered a nice online multi-player game: Age of Pirates. AoP is in a certain way similar to one of my favourite games Age of Empires, available as an offline game. In AoP, you have an island on which you have to gather resources in order to improve your economy and military activity.
When you have a certain grade, it's possible to create ships and to colonize other islands. There, you can crop cacao, hemp and other goods which you can trade with other players for money. Also, you can attack other player's islands and plunder their resources. And if your fleet is large enough, you can even takeover the island and incorporate it in your empire.
Anyway, the graphics and gameplay are very nice for a browser-based online game. The only disadvantage is that some translations are unfinished (a lot of German phrases in it, Capitän :-)). Another disadvantage is that you have to build an enormous economy prior to being able to build ships. But hey, it keeps me playing!