In the UK: Cabair has the best reputation, most UK airlines, including now also BA send their cadets there.
Oxford is also good, BM trains their pilots at that place.
In the US: Flight Safety in Florida, watch out for a lot of dubious schools offering cheap courses, but no quality... I also think Comair has a good school, and Purdue (Purdue arrow&cadet might tell you more about it)
In the Netherlands: NLS (Nationale Luchtvaartschool), KLM (KLM School), EPST (training at Cabair and MCC-course at ATP-academy, they guarantee you an immediate entry into a UK Airline on Boeing or Airbus as FO!)
Belgium: SFA (Sabena Flight Academy, maybe the best of them all)