Half a Dozen Birding Mysteries

There are a LOT of birds that I see that I can't identify, but most don't get photographed.  These are the lucky ones.  Above is an Empidonax flycatcher species, which I think might be a Least Flycatcher.  Does anyone disagree with this, and if so, how do I tell what it is in future?

I found this gull on the right in a group of Ring-billed Gulls, like the one on the left.  It's a bit smaller, and its wingtips seemed oddly colored with the line and dot patterning.  I have no other photos.  Is it safe to assume that it might just be an oddly-patterned Ring-billed Gull?

This bird, just over or around the size of a Blue Jay, flew past me at Marine Point.  This is the only photo, as it vanished into the trees at the end of the point.  It flew mostly in a straight line.  I don't know what species it is, but the wingtips and dark cap seem unusual.

This is the back of a rather unusual flycatcher I found at Chatham Wildlife Sanctuary:

Is  this just an uncommonly dark form of the Eastern Wood-Pewee, or is it something else?

And then there's this sparrow I found skulking in the weeds on the observation mound at Nipper Wildlife Sanctuary.  I have provided all the photos I took of this bird, which vanished into the weeds shortly thereafter.  Thoughts?

Accompanying the bird above is the bird below.  This bird below was small, almost Carolina Wren-sized.  If not for the short, stubby bill,  I would have assumed it was a wren or maybe a warbler.  The lake of wing bars and generally shy demeanor keep me from calling it a goldfinch.  I'm guessing this is a female or a juvenile of something I know better in another plumage.  Any ideas?

As I'm posting this in IBET, please email me or comment down below with thoughts and ideas.  Also, so I stop spamming IBET with ID questions, what are some good ideas for resources to identify these birds?  I've used field guides on these, to little avail.  I've heard of a Flickr group that identifies birds based on submitted photos.  Any other ideas?