The titles and forms of address found here should only be used in the most formal of situations. Often a priest will laugh and tell you to call him by his first name (or maybe Father), but you don't want to insult a man of God (unintentionally at least).

Archbishop:
Address on Envelope - `His Grace the Archbishop of _______'
Begin Letter - `My Lord Archbishop'
Close Letter - `I remain, Your Grace, Yours faithfully' or simply `Yours faithfully'
Spoken Address - `Your Grace' (use capitals when you speak to them, they can tell when you don't)

Bishop:
Address on Envelope - `His Lordship the Bishop of _______' or `The Right Reverend Such-and-Such of _______'
In Ireland use `The Most Reverend' instead of `The Right Reverend'
If an auxiliary use `The Right Reverend So-and-So, Auxiliary Bishop of _______'
Begin Letter - `My Lord' or (in formal situations) `My Lord Bishop'
Close Letter - `I remain, My Lord, yours faithfully' or `Yours faithfully'
Spoken Address - `My Lord' or `My Lord Bishop'

Canon:
Address on Envelope - `The Very Reverend Canon So-and-So'
Begin - `Very Reverend Sir'
Spoken Address - `Canon Whats-His-Face'

Cardinal:
Address on Envelope - `His Eminence Cardinal of _______'
If an Archbishop `His Eminence The Archbishop of _______'
Begin - `Your Eminence'
Close - `I remain, Your Eminence (or `My Lord Cardinal'), Yours faithfully'
Spoken Address - `Your Eminence'

Clergy:
Address on Envelope - `The Reverend Such-and-Such' (if he's a member of a religious order include its initials after the name)
Begin - `Dear Reverend Father'
Spoken Address -- 'Father Whats-His-Face'

Pope:
Address on Envelope - `His Holiness, The Pope'
Begin - `Your Holiness' or `Most Holy Father'
Close - (if you're RC*) `I have the honour to be Your Holiness's most devoted and obedient child' (or `most humble child')
Spoken Address -- 'Your Holiness'


*and if you're not Catholic, then you pretend you are.