Dave, one of the things I have used with success is your wifes favorite non-stick spray - Pam. I don't live in the rain forest but it works great here in the desert where rust can also be a problem.

Try some anti-seize. That stuff will withstand almost anyhing.
Mike

Did none of your other "recipes" work or are you just looking for other alternatives? I find it hard to believe you still got rust with all of the other things you've used. I've used most of those listed with good results in the Seattle area. I just use whatever is handy at the time therefore the coating is different from tool to tool. One exception is my table saw which gets paste wax to prevent rust, keep it slippery and so it doesn't transfer to the wood being cut.

I don't use cooking sprays since they almost all contain water. You'll end up with water suspended in the oil and you'll still get small bits of corrosion. For a shovel, it's not that big of a deal but for other "good" stuff I wouldn't use it.

For rust prevention and also to keep snow from sticking to the plow on my truck, I use paraffin wax. This also works great for metal snow shovels, especially when the snow is slightly wet where it will stick to an uncoated shovel. If you're concerned about the wax being a petrochemical product, you could use beeswax or other organic materials such as coconut oil.

To apply paraffin to a shovel or other tools you could use a hair dryer for heating the surface where it will flow easily. It's best if it is applied with heat, since it will fill in any pores in the metal, and will smooth out nicely without much wax required.

The last time I waxed my plow was about 4 years ago, and I might consider redoing it again this year. It gets used pretty hard and the wax job has held up well.

GG

I use Sheath, a protective spray on oil for firearms. Available at WalMart, sporting goods stores, or gun shops. Rem-Oil and similar products work well.

If they're already rusty spray them with Duro Extend, Naval Jelly, or one of the other rust neutralizers. The rust will turn black. Works great. Extend is sold at Home Depot etc.

Use Boiled Linseed Oil - BLO - not raw oil on wood. Be careful with the rags as spontaneous combustion can occur.

For garden tools I use boiled linseed oil on the handles and spray paint on the metal parts. (I usually treat them at the end of the season)

I know spray paint on shovel blades doesn't last that long but I usually have some surplus or closeout spray paint and it help prevent rust thru the winter.

For non stick surfaces like mower decks, rototiller hoods, and spreader hoppers I use Slip Plate #1. It's a heavy bodied graphite paint but it's as close to a Teflon like surface you can do yourself.

Boeshield T9 ( The best ) for all metal surfaces. - Kris

I dont want to hijack this thread but I figured someone here might know if some of the products suggested here remove old rust from a more delicate slightly rusty item (IE: old carpenter framing square without scracthing all the lettering) Most tools and old steel come back with a grinding of some kind sanding etc. but I would hate to scratch this item all up. Please comment on your experience.
In the mean time I will try some of the things already suggeste have used T9 pretty good stuff.

vinegar (acetic acid) works as a mild rust remover

I've used it on cast iron cookware and lightly rusted steel with excellent results.

Naval jelly will work too, but it's a bit more corrosive since it contains phosphoric acid.