Are you looking for a super-simple quick reference for WP_Query and all of its parameters? Loosely described, WP_Query is how WordPress displays posts defined by a variety of parameters, and keeping that of the available parameters can be a monumental task. It’s easy to forget all that you can do with WP_Query if you aren’t working with it every single day.
Of course, this brings me to this handy Gist. It’s nothing flashy, but it is a super-simple text file listing and describing all the WP_Query parameters. I’m not sure how long this will be around, so you might want to download it ASAP for reference when you need it.