Forget the Irony range and look at Originals and Skin instead.  The plastic Skin watches are completely sealed on the back in plastic.  Most of the Originals are plastic backed with the exception of just the battery.  If your allergy is just to nickel and not all metals then we have been advised by customers that Swatch watches are particularly suitable because they are made of stainless steel.

New for 2006 - The Jelly in Jelly range is completely finished in plastic, even the battery hatch.  There are no metal parts to come into contact with the skin at all.  To view the range, click here.