My favourite album to chill out to is definitely Disco Volante by Mr. Bungle.
Actually, no. My favourite chill out album is probably any The White Birch by Codeine or I Could Live In Hope by Low. "Slowcore", as some call it, is great to chill out to.
Lou Reed's Metal Machine Music is definitely not a chill album. I've never heard of anybody going to listen to Metal Machine Music to unwind after work or something.