[Gorwingel]

Frodo, Sam, and Bilbo were ringbearers (Sam though for a short time)
Gandalf was a ringbearer too, though of a lesser ring.
Legolas asked, if I recall correctly, Galadriel, because Gimli was a friend of the elves, if he could come to the havens too.
Aragorn was king, so he had to stay with his people
Arwen choose not to go to the havens
and Merry and Pippin were just simple hobbits with no reason to go.
I could be wrong about some of my reasons, but I think I am pretty close.