I'd like the ability to create a schema for multiple database types such as MySQL, SQL Server, and PostgreSQL. I know ORM tools such as Hibernate can do this, but I won't be using an ORM to access the database so would like a solution that doesn't depend on one. Are there any tools that can do this?
Edit:
I forgot to mention that this is a personal project so I'm looking for something either cheep or free.
Take a look at Erwin.
Edit: (Based on question update)
Yeah Erwin is not going to be cheap. I did a quick search and found Toad Data Modeler, which I haven't tried but may be worth looking into:
Entity relationship diagrams - both Physical and Logical modeling (incl. inheritance)
Support for various databases (Oracle, MS SQL Server, MySQL, Sybase Ase, PostgreSQL, DB2)
Generation of SQL (DDL) scripts
PowerDesigner is a far better choice than Erwin but it too is expensive.
It took me roughly 16 hours to install the demo of Erwin, lots of failed attempts, incomprehensible error messages, help phone number which were disconnected.
PD will give you 14 day free trial.
SQL Power offer a FOSS modeling tool, SQL Architect. It can generate DDL for several flavours of database. It is still technically beta (current release is 0.9.1) but it should be fine for a personal project. Find out more.
I know you said u don't want an ORM but SubSonic 3's migrations might just do the trick for you. You don't have to use the ORM just have SubSonic build itself from your database and have it as a separate class library. Then change the provider say from MSSQL to MySQL and have it rebuild itself.