Among the many catastrophic signings of Madrid I would say, for example, Manuel Canabal and Elvir Baljic.
Canabal was a very tall and clumsy striker who Capello wanted and cost 800m pesetas (Suker cost 600). Testimonial presence in the team.
Baljic, the "Rivaldo de los Balcans",high expectations,and a very expensive transfer:3500m pesetas(20m€in 1999) while Barsa paid 4000m pesetas to get Rivaldo just 2 years before.
He didn't do anything special and later had a ACL injury.
In Barcelona, and out of the usual candidates I would say Ciric, who was supposed to be a mega top midfielder and Geovanni, who barely played and was very expensive