The differences between the C4040 and the C5050 are the following:
multiple media support: compact flash, smart media, microdrive and xd picture card.
photo assist lamp
moveable lcd panel
hot shoe for external flash
If budget can afford the C5050 that would be my camera choice. I own the C4040 and it is an excellent camera with the same optics as the C5050. You can view some of my photos at: