There is a limited choice of Data Dictionaries available, and they are all rather expensive, (eg $250,000).

They are usually available as part of a larger ETL or Migration Product.

We use one we developed in-house, which is available on-demand.
We updated this page in May,2010 and discovered some pages have moved but prices were still difficult to find, which implies that most products are still expensive.
We hope all the links work for you, but if not, we would be very pleased if you could tell us about broken links you encounter, so that we can fix them.