What CDs do you use to evaluate gear, systems, etc

There are many threads on the Audiogon which will answer you question.

In my opinion one of the best way to evaluate a system/component is to use music which has plenty of acoustic instruments. I use it regularly and I am more than stisfied with what the results are vis a vis what I am looking for. You may do a search on your own to find many such threads, I quote just one example here:

Best acoustic -natural instruments CD's

Chris Isaak...Forever Blue...for soundstage depth
Massive Attack...for deep bass and transparency
Pink Floyd...for imaging...

Here is what I use...

Rebecca Pidgeon's version of Spanish Harlem on Chesky album 'The Raven'.
Suzanne Vega's Jim's Diner on Solitude Standing.
Those are great solo voice.

My acid test is Henryk Gorecki's Symphony #3 for low level resolution at the beginning, great dynamic range and Dawn Upshaws spine decalcifying highs.