I personally use an old can of Smith's Honing Oil, mainly because I use it sometimes when sharpening anyway. It's mineral oil based, and I don't know that it's much else.
I am very eager to try nano oil though, I hear it's in another class as far as smoothness, though I wouldn't know personally.
I am also interested in Froglube, both as a lubricant and rust inhibitor. It performed very well in Loonybin's
Rust Prevention Test, and it's food safe to boot. Most of my knives are non-stainless, and I'm hoping to grab a few Japanese Kitchen knives in what I hear is very reactive Hitachi White steel, so rust prevention and food safety are also on my list. A product that covers all these bases is hard to pass up.
EDIT TO ADD: I can also vouch for Graphite powder, I use it as a lubricant when I can get a hold of it, I actually prefer the feel over mineral oil. In my experience, however, it doesn't last as long per application as the oil (could just be my imagination).