Microsoft Word 3.01 and 4.x with the US dictionary (and maybe UK?) 

Spellcheck the word "childcare".

The spell-checker will suggest one word: "kidnaper" [sic]. (Contributed by Adam Shostack)

Also, try spellchecking "supression" [sic].  (Does this work on Word 3 too?)

The spell-checker will include "Cupertino" among its choices. (Could this be secret Apple-bashing? ;) 

(Contributed by Hiroki Morizono)