Here is another way to do it if you want to use ViewData:
@Html.Partial("~/PathToYourView.cshtml", null, new ViewDataDictionary { { "VariableName", "some value" } })
And to retrieve the passed in values:
@{
string valuePassedIn = this.ViewData.ContainsKey("VariableName") ? this.ViewData["VariableName"].ToString() : string.Empty;
}