Dear Raul,
I think that what you need is a many-to-many relationship. You have many products related to many posts. For this you will need an extra custom post type that acts as an intermediary. This post would be child of both products and posts. This way you will be able to add several products to each post using a dropdown. Its explained better here:
http://wp-types.com/faq/how-do-i-associate-one-child-with-several-parents-of-the-same-type/
Please let me know if you are satisfied with my answer and if I can help you with any other questions you might have.
Regards,
Caridad