I'd imagine some of Godin's finer models will become very well-regarded in 20 years, now that they're finally making an aesthetically pleasing guitar. Fenders, too -- the current crop are very nicely made, thoughtfully designed guitars, from a brand that is synonymous with the electric guitar. Larrivee and Breedlove acoustics.
Ampwise, a lot of the boutique stuff will hold its value -- BadCat, Matchless, /13, Suhr. I can see the modern Traynors becoming legendary very soon, if only for their low used value and decent tone. Simple, well made tube amps pretty much never go out of style. The Peavey 6505 is definitely a standard in the heavier realm. I doubt anything digital will hold its value, only because of the constant improvements.