Differences between the Harry Potter and the Goblet of Fire film and the book:
House elves and S.P.E.W. are cut out
Ludo Bagman is cut out
Bertha Jorkins is cut out
Barty Crouch Jr's confession is cut out
Barty Crouch Jr's fate is cut out
Harry's recuperation in the hospital wing is cut out
Fudge giving Harry's winnings to him is cut out
The creatures in the enchanted maze are cut out
The Dursleys are cut out
Hermione's capture of Rita Skeeter is cut out
Several Pensieve scenes are cut out
Sirius Black's role is very small, compared to the book
The Quidditch World Cup match is cut out

Etc., etc. For more info, see Wikipedia.