It sounds like you want to create a custom editor part. In the part you would have one dropdown that shows the names of the lists (you probably want to filter hidden and empty lists) and, when an item is selected from the list, a second dropdown shows the Title column of the items from the selected list.
Here's some code (edited here, so it will need to be cleaned up) to help you get started:
protected Page_Load(...)
{
if (IsPostBack) return;
var web = SPContext.Current.Web;
var query = from list in web.Lists
where list.Hidden == false && list.ItemCount == 0
select list;
DropDownList1.DataSource = query;
DropDownList1.DataTextField = "Title";
DropDownList1.DataBind();
}
protected DropDownList1_SelectedIndexChanged(...)
{
var web = SPContext.Current.Web;
var listName = DropDownList1.Text;
var list = web.Lists[listName];
var table = list.Items.GetDataTable();
DropDownList2.DataSource = table;
DropDownList2.DataTextField = "Title";
DropDownList2.DataValueField = "ID";
DropDownList2.DataBind();
}