Previous post from Don Pistulka:-
Formula (Array - trl-Shift-Enter
=ADDRESS(ROW(OFFSET( $A$1,COUNTA($A$1:$A$65000),0)),COLUMN(OFFSET(
$A$1,COUNTA( $A$1:$A$65000),0)))
or
Macro:
Sub NextBlankDown()
Range("a1").Activate
If ActiveCell.End(xlDown).Row = Rows.Count Then Exit Sub
MsgBox (ActiveCell.End(xlDown).Offset(1, 0).Address)
End Sub