Best wild bird to protect an orchard from bugs?

What is the best wild bird for snatching up bug pests that infiltrate pear and apple orchards? I would think some sort of swallow? I live in the Pacific Northwest, in the Columbia River Gorge (so would need to be a species found around here).

Anyone built nest boxes/birdhouses to attract them? How'd that go?

Regardless of the species, you will want to attract them, and keep them.
One of the best ways to attract them is through native wildflowers.
The birds will go where they know food will be found, and wildflowers are like magnets for birds.

Here is a link to a variety of nest boxes: http://www.extension.purdue.edu/extmedia/FNR/FNR-246-W.pdf

An often overlooked factor in keeping the birds, once they have been attracted is water.
Like any other animal, birds need water for survival. Without a source of clean drinking water, they will not want to set up nest in any location. By providing water, you are greatly increasing your chances of keeping the birds on your property, rather than the neighbor's.

I am at the western end of the gorge (Camas).

This winter I tried something new - throwing wild bird seed (black oil sunflower) under my apple trees, every day. Here is my logic with that - codling moths overwinter as a larva in a cocoon, in bark crevices or in the leaf litter under the tree. I noticed that when I throw bird seed on the ground, it is the birds' natural instinct to scratch the ground, even though the seed is sitting on top of the ground. When I throw the seed under my apple trees, they happily scratch away for hours. I theorize that during the winter, if a bird is scratching away and uncovers a larva, they will gobble it up - e.g. my suet feeder is much more popular in the winter than at other times of the year, so birds must prefer fat/meat to seed in the winter? Even if the birds don't eat the larva, they will be exposing them to the elements which will probably make the larvae unhappy and might even kill them? Anyway, because I put seed under my trees every day all winter, there have been hundreds of birds scratching around under and on the tree all winter, hopefully making the codling moth larvae extremely unhappy. In the fall I will know if I have fewer codling moths this year.

The other thing I do with codling moths is plant (or not kill, if they volunteer) perennial flowers which attract parasitic wasps - yarrow, mint, queen anne's lace.

The species which seem to do the most scratching are Spotted Towhees. They like to hang out in brush piles, so you might want to provide some of those. I don't think they have ever used any of my nest boxes but I haven't built a box specifically for them.