Where can I find ready-to-use database models ?
I don't need a database with data in it, but only schemas (UML diagrams). Perhaps something like the data models at this link, but much more complex and real world.
Michael Blaha's Patterns of Data Modeling. This one has some interesting temporal, graph, and tree models.
Martin Fowler's Analysis Patterns. This one skims some of the other patterns, but gives accounting a solid treatment.
They are all well-rated, and I have read all but one, and they are all very good. Several of them are available on safaribooksonline.
Also, OASIS's Universal Business Language schemas (xml)
What are you trying to do anyway?