The name is derived from 'God's Friday' in the same way as good bye is derived from 'God be with ye'.
In Germany, the Friday before Easter is called Silent Friday, and in Greece, Holy or Great Friday.
Good Friday Superstitions
Friday 10th April 2009 - What is Good Friday?
Sunday 12 April 2009 - Easter Sunday / Easter
Monday 13 April 2009 - Easter Monday