If you have one of the newer DSLRs that allow you to fine tune the focus calibration on individual lenses, you may be familiar with the frustration involved in setting up some form of calibration device.

This new product (not cheap but should last for ever) looks like it will do the job. They are out of stock already, but I have placed an order.

http://www.rawworkflow.com/lensalign/

Of course, you could always make one, for a lot less than 85 Bucks

Plenty of free focus charts on the net, combine with a scale set at 45^o QED

That's what I use now, but it takes an age to set up, and I am never really sure it is properly aligned.