This is quite a hardship area to catalogue as there are a large number of ad-hoc cards produced. This list is nowhere near complete and mainly focuses on the mainstream 'officially' produced items.
The definition of a Postcard is a bit subjective, mine is a single printed card with picture on the front with blank message and postage details on the back (sometimes Greetings cards are classed as Postcards, I am not including those here).
There are also a lot of printed picture cards which are often promoted as postcards, which I haven't included.
There are also a lot of 'unofficial' postcards from Asia, also not included.
These contain pull out individual postcards within them.
Tolkien's Middle Earth
The Lord of the Rings
Tolkien's Middle-Earth & Monsters
The Tolken Artwork of Greg & Tim Hildebrandt
Calendar with Postcards
Lord of the Rings
Bodleian Library Manuscript Set
Bodleian Library Tolkien Drawings
Come with the Hobbt 75th annversery pocket edition.
Tolkien Portraits Set (Pamela Chandler)
Robert Rosenthal Hobbit
Peter Pracownik (Artist)
Bakshi DVD set
Free with limited edition DVD package
Lord of the Rings Musical
Movie Fan Club Exclusives
Two Towers set
Air New Zealand
Hobbitton Film Set New Zealand
Lord of the Rings Movies
Unexpected Journey movie
These are postcards featuring stamps
Isle of Man
Return of the King
Puffin Hobbit (Pauline Baynes)
Bilbo's Last Song
Barnes and Noble
Film tie-in book promotions