RemyRAD, TVPostSound, and I were discussing reference CDs in another thread and (for one reason or another) I thought it may warrant it's own topic.

So, what CDs do you check your mix against? What great albums do you use to setup your mixing environment? What is your reference?

What is the best sounding CD available (any genre) in terms of recording and mastering job out there? I know opinions will differ, but I an wanting to buy a CD to use as a learning too (listening and learning about what I should go for in terms of sound).