CT90 for steel, only because it's what my local emporium stocks rather than scientific selection. Bit pricey, but it seems to work better than DIY alternatives, and a bottle lasts ages.
White paraffin or WD40 for Aluminium. Diesel is too obnoxious for me!
Almost anything greasy or oily is better than nothing. The advantage of CT90, Rocol and Co is they contain high-pressure lubricants and are human and machine friendly. As cutting agents I've no idea if they're ten times as good or only slightly better than bacon fat, but at least they don't go rancid!
Dave