Database schema document creator [View all]

I am in the market for a CRM system and want to create a database schema in advance so that I can document the fields I need as well as the relationships to make sure that I can setup/modify whatever is out there to compare.

Any recommendations on an application that will allow me to do that?

Don't really need the full monty (data field types, etc) as I am the only one that will be using it as a reference - just a table/field chart showing relationships - I'll know by the field names what type of data is being captured.

Help?