Generally, RushPcb Inc can handle board size up to 20in x 24in, however our optimum working panel size is roughly 12in x 18in for sample runs & 18in x 24in for medium to large PCB production.
In small quantities (Less than 25 units or so) panelization is not a critical item, but it is helpful with very small board sizes and with higher volumes.
In certain instances, our Short-Run Production service does require panelization.