Sea types

Simple- As I said before this is basically just a grid plane. It's useful for making lakes, ponds, etc. DO NOT I repeat DO NOT use the simple mesh type for oceans. You will see the edge of the plane in the horizon!.
The left picture is one using the simple mesh and no DS sea bump map. Everything in the center picture is the same, but this time with the DS bump map. What an extreme difference ehh?
Finally the right one is with a lot more wave speed, etc and foam turned on.

Adaptive- Now this baby is the shiznit. Notice on the Simple mesh you can see the edge of the plane. Well this can either be an infinite plane or you can base it off what the cameras FOV is. Also notice that the ocean goes all the way to the horizon because it's an infinite plane.

You're probably thinking: "What does it looks like when its animated?" Well, the motion of the waves is very realistic. Here's a quick movie of an animated sea. One of the great things is you don't have to calculate the wave action, its all done for you. All you have to do is tweak the settings until it looks good to your eye.

 Sample Animation