I'm looking for a good tool to help me draw ER (entity-relationship) Diagrams on Windows
I use MySQL Workbench on OSX, and they have a Windows version as well. Quite nice (to me, at least), though it is my first and only ER Diagram tool.
Enterprise Architect is good. Allows you to generate DDL create statements. It's a commercial product, so there is cost here.
I've used Visio to do that in the past, you might check out: http://office.microsoft.com/en-us/visio/HP010181611033.aspx
There's also Dia which is open source. I'd imagine you could put together a diagram using their included shapes/symbols.
I recommend MySQL Workbench. Not only you can draw database ER with it, you can also instantly apply the changes you make to the actual database from within the application.
MySQL workbench is a nice tool for MySQL design. BUT BEWARE !!! On my Linux box it surely crashed after clicking on 'NOT NULL' column and somewhere around of it in the field editor window. At least this applies to the version I downloaded in July.
But this is also a nice free tool for PostgreSQL design beacuse there is no such free design GUI for this DBMS. You can read a little bit more here: http://allarounddb.blogspot.com/2009/07/er-tools-for-postgresql.html
SchemaCrawler is a command tool that can generate E-R diagrams. You can exclude tables and columns using regular expressions. It is free and open source.
Try SchemaBank, they are web-based SaaS provider on database design. You can use whatever browsers on Windows to do the job, pretty cool!