I don't know what OS you're using, but I recently went through the same
search on a very tight budget (free). I ended up using Visio because I
already had it. I have Visio 2002 but found out that the standard
version that I have won't connect to an ODBC DB and generate an ERD.
However, the Pro version will. In my case, I ended up biting the bullet
and creating everything by hand. My DB only has 41 tables, so it wasn't
as bad as I was afraid it would be.
I also used the trial version of EMS PostgreSQL Manager. It was OK. I
really only used it to create a diagram. It did create the diagram.
But by the time I rearranged all of the tables so that the lines
representing my FK's weren't crossing and the whole diagram fit on an
11x17 sheet of paper and was still big enough to be legible - it ended
up taking about the same amount of time as it took me in Visio to create
the whole thing myself.