So. I'm originally from New England. We get 30-40+ inches of rain per year, so the only constraint I consistently pay attention to is how cold-hardy something is.
I'm down with all of the water capturing and retention tecniques, e.g. hugelkulture, berms and swales on contour, rain barrels, mulch, MORE organic matter, nitrogen-fixing trees etc. Beyond this, I want to expand my list of useful plants that specifically don't need a TON of water *and* are cold-hardy (Zone 5a). I just bought "Drought Tolerant Plants" at a used book store, but it's aimed at people that like ornamentals and lawns.
Apricot, Filberts, Oregon Myrtle, Almond, Jujube, Autumn Olive family, Mulberry, Beautyberry, Gooseberries, Grapes, Walnut, everything in the mint family (mint, thyme, oregano, etc).
With the amount of rain that you get you really dont have to worry about rainfall, just planting at least 25% of your garden at Nitrogen fixers, an mulching to feed the fungi an cut down on soil evaporation