Alignment change has no special effects in 3e.
If you were the cleric of a LN, CN, or NG deity, switching to NE would require you to change to a new deity. If you "grossly violate the code of conduct" expected of your particular flavor of cleric, then you must atone. Other than that, any penalties that apply are purely the DM's judgement.
(Personally, I would definitely require some kind of atonement if the cleric were switching between turning/rebuking, or if the alignment switch forced him to change his domains. That's just me though.)