Blue-gray Gnatcatcher

Blue-gray on top, white below, this little guy is only about 4" long, including the tail! "The long (thin) bill ... the white undersides ... the long tail with white outer tail feathers, plus the bold eye ring are a dead give-away" says our friend, John Jones.
Ruby-crowned Kinglet
Notice the eye ring - it's on

the SIDES of the eye, not top-and-bottom

nor all-around.