Some of the images I found for Vireo look promising. I'm glad to know it's not a woodpecker; I'd rather avoid the soundtrack. :-)

We have a lot of robins here, but all the ones I've seen are brown (with the red breast), and everything I can see on this bird is black/gray. I can't see into the nest without using a ladder, so I haven't tried that yet -- I don't want to scare off the mom-bird and have her abandon the eggs/chicks. (I don't know if that would happen; I know almost nothing about birds. So I'm being cautious.) If I see the nest empty (during daylight) I'll try to get a look then.