I saw that mystery bird again--not the one I ID'd as a red-bellied woodpecker (that really was a RBW female), but the bird I actually saw the first time I saw the mystery bird. Apparently, I've been seeing two different birds.
Yesterday, I saw the original mystery bird again--no red on the nape, the ring-like thing around the neck, the stripes on the back--the way I remembered it in my initial description. Here is a really horrible drawing on MS Paint:
This is really bad--and the text is too small to read. But basically, the wings are stripey, there's a definite white stripe/patch on the back between the wings, and the nape and face--well, you can see why I thought it was a ring now. But it was more of a mask-like kind of thing, two of them actually, extending onto the face (I think). Didn't get a great look at it, but I did see it long enough to note the complete LACK of any red on the back of the head/nape.
Thus I ask you--what is this bird? The downy, hairy, and red-bellied woodies all have some red on the head. This one had nothing but black and white all over. Definitely clung to tree and moved very fast around the trunk. About the size of a cardinal.
Further--the chrysalis is soooo close. I hope he's just starting to eclose when I get home, but I may miss him. I got a great picture last night, which I'll post later this evening (it's at home, still on the camera).
UPDATE! Per my birding friend Roana, it's a female hairy woodpecker!