Motor oil works fine. For more delicate stuff like firearms, light oils like "Rem Oil," which comes in a nice spray can is excellent. For longer term storage, I like Hoppe's Rust Inhibiting grease. Just apply with a rag in either case.

WD-40 (let the flames begin) is basically kerosene and some sort of solvent carrier. Nice for cleaning stuff up, but minimal rust inhibiting qualities.. I live on the DE shore, and salt air is not your friend here. I take all my tools off of the tool board/tool boxes about once every 6 months and wipe them down. Saves a lot of grief.

I have used Naval Jelly on really bad cases, but in general, oil and fine steel wool seems to be satisfactory. If finish damage is a possibility, I believe some people suggest bronze wool, which won't scratch as much.

For some stuff, I've used "Instant Cold Gun Blue" to put a more permanent finish (you still need oil) on some small tools.

/paul W3FIS