If not a Silmaril (like somebody said, too dangerous), then a Palantír would do fine. Not for using it to communicate (we have internet for that nowadays), but just for the sake of it. I just think it's a very beautiful object. And if it was the palantír of Orthanc, then also because of the people who used to wield it! (Namely, generations of wise Gondorian men, and most of all, Saruman and Pippin
And briefly Gandalf. I don't care about Aragorn.) And I could use it to look around the world, just randomly, here and there, but probably just whenever I would feel like it (seems it was rather exhausting business). For this reason it probably also should not be the palantír of Minas Tirith, like Gandalf said, wouldn't exactly like to see that...
EDIT: Oh, but then there is of course Tuor's cloak. But then again, it would not last very long, I presume... so the Palantír is better in the end, I think.