WD-40 is technically a “Water Displacement” tool, and not a rust preventative.  Using the products BELOW would be a better choice, but WD-40 is so common that it deserves mention for dealing with rust.  Whether you have a can in the house or need to run to the local hardware store, it’s a quick temporary solution.  WD-40 does a fairly good job as a penetrating oil and at displacing water.  We use WD-40 on rags or with a scotchbrite pad to clean up tools or parts with minor rust. 

Buy WD-40 Here

LPS 3 is an excellent rust inhibitor and is the primary tool we use at Saunders Machine Works.  We spray a light coating on to the part, vise, machine table, etc – whatever surface you want to avoid rusting – and then we will lightly spread it around by wiping with a clean paper towel or cloth.  LPS 3 dries to a lighty waxy film.  NOTE: LPS 3 is a completely different product than other LPS products (e.g. LPS 2!)

Buy LPS 3 Here

Crown Tool & Die Saver 3090 is easier to apply and less messy than LPS 3 and dries to a thin film. We've found this to be great for long-term storage when parts and fixtures aren't in use.

Buy Crown 3090 Here

Lanolin is a wax that has a variety of uses, including being an excellent coating to prevent rust. It is also incredibly easy to source as it is a normal household product. Lanolin is thicker than liquid rust preventatives and stays in place.  We use it in places like cavities in our CNC vises that we don’t want to rust.  A liquid rust preventative would more quickly wear off, but a light coating on lanolin lasts.

Buy Lanolin Here (also available from McMaster-Carr here)