Amazon (.de) is giving away 10 EUR discounts if you order Mac OS X Leopard v10.5 before 1.11.2007. Just go there and enter following code to your order: AMZNLPRDAPPL.
It’s Amazon Germany and the code is probably only valid there.
I personally will wait until all the “Leopard shredded my disk and drank all my beer” whining is gone and the system is stable and ready for productive use. So let’s say starting with 10.5.2.