I spent last weekend at my parents' house in Monument Beach on Cape Cod. My dad had to work on my car, and it was great because while I was at the house I noticed some yellow-rumped warblers in the side yard on the border of the conservation land.
The only warblers I saw were yellow-rumped, except for one mystery warbler. It was very small (4.75" or smaller), and all yellow except for a gray mask/hood. The gray went on either side of its face. I only watched it through my binoculars- by the time I got my camera up it was already gone and I didn't see it again the rest of the weekend. There are so many yellow and gray warblers that I knew my odds weren't good. I guess I can just hope I see it again so I can positively ID it.
Picture of yellow-rumped warbler:
There were many female yellow-rumped warblers in the yard too, but I didn't get any pictures of those. They're actually very similar in appearance to males, but are just slightly more drab in color.