The tiny Psaltriparus minimus is only about 4 inches long, including its tail! You can see it here perching on a plant with its little claws. (Click on the picture to zoom in for a better view.)
This bird looks a bit like a wren, but it's not. In fact, no other birds are closely related to it—it's the only species in its genus. There are 13 species in its family, Aegithalidae, but this is the only one in the Western Hemisphere; the other 12 live in Asia and Europe.