I found this link today - http://www.sommarskog.se/dynsearch/Northgale.sql
ok I know I am a bit late most of you will probably know about it ;)
But it is simply great. It uses an existing Northwind database to generate the same tables inside Northgale but with a lot more data. For exmpla the order details table ends up with more than 2.3mln rows!
When I tried to select from order details all rows with quantity > 30 it took 13 seconds!
What can be better than that to allow you to experiment with your queries when you're looking to improve performance?!
I think the only requirement is a northwind database and it takes just about 5 minutes to setup.
I hope someone some day will discover this post and will find it useful ;)