How to preserve value of Page's property between postbacks?

Thanks, Roei.

HttpContext.Current.Session[] seems more convenient to me, because ViewState requires serializable data.
But both seem almost as cumbersome as having custom repository class for just passing values between instances of Page.

Is there a way to preserve previous instance of Page and pass it to the next instance in property?

PreviousPage contains previous instance on cross-page Postback, but it's empty when Page posts back to itself.