It depends on how often you use them I guess. For tools that are small enough, an oversized ziploc bag (they make them that are up to 24" x 32") and couple of desiccant packs will do just fine, as long as the bag remains sealed. Desiccants Packets.
I live on the Alabama Gulf Coast, and down here the humidity is truly awful. My garage is not heated or air conditioned (but a man can dream....) and any raw exposed steel will rust if not protected. None of my small power tools seem to suffer from the humidity. But it's just damp air, not actual condensation.
DirtyDog has it right. Spraying WD40 into an electric motor on a drill or saw isn't going to hurt anything and it will definitely help prevent corrosion.
Larger stuff is a harder proposition.
I just finished re-habilitating an old Harbor Freight wood lathe that lives in my garage, the ways and other exposed raw steel parts had a liberal layer of surface rust. It came off with wire cup on an angle grinder, and a little sweat, but to prevent it happening again, I'm trying a light coat of machine oil, we'll see how that goes.
Again, it depends on how often you actually need to drag them out and use them. If they are going to be stored and idle for a long time, it's hard to beat Cosmoline. The miliary has been using it for decades. It is incredibly effective, but it is also a PITA to remove when you drag the protected item out of storage and need to use it.
As EastCoastMoJo said, improving ventilation will also help. Alternatively, if you have power in the shed, you could take the opposite approach by making the shed reasonably airtight and putting a small dehumidifier in there (with the drain plumbed to the outside of course...), but that's the "nuclear option". :)
Generally speaking, electric motors are unlikely to have trouble resulting from normal condensation, as long as they are reasonably dry when you power them up.
I'd probably go with a combination approach. WD40 for the motor internals, Bag or saran-wrap the parts you can, and a thin coat of light oil (like 3-in-1 Oil) on exposed raw steel.