I knew about them (but not about the ones that pwcosol showed in the first post) only because I saw a picture in the Brett's book.

I think I am going to have to get Homer Bretts book, would you happen to know the title of it Carlo?

Here you are
http://img14.imageshack.us/img14/3640/brettn.jpg

I see there are several copies available on ebay, the cheapest is around $65.
Perhaps you can find it at a lower price.
Don't expect hundreds of pages on the M9 (but most variants are covered). Still a very nice book with small captions but really beautiful pictures.
In my opinion a must have.

I agree with Carlo. HB's book is a "must-have" reference if you are interested in bayonet/knives in general. IMO, it also covers a large number of M9 bayonets, which makes it the most informative on the subject thus far in print (The book "American Gladius" notwithstanding with it's detailed coverage on a few very specific patterns).