What's your favorite "cheese" sauce?

First off - yes, I've checked the memories. I found a number of great looking recipies for "cheese" sauce. However, I'm wondering which one(s) is(are) your favorite(s)?

The other day I finally picked up some nutritional yeast and haven't done anything with it yet, so thought I'd try making a "cheese" sauce to serve over steamed veggies.

Any input will be appreciated.