Many species are self sustaining, and you'll seldom see them at your feeders — robins, for example, feed almost exclusively on insects.
But there are plenty of other species that rely on the kindness of strangers, especially during the winter months. Chickadees, nuthatches, and sparrows winter over in the Northeast and will be frequent visitors to the stocked Northeast feeder.
But every so often, the patient birder will be rewarded by a glimpse of some of the more colorful and not-so-common diners sampling feeder fare.
Goldfinches are smaller than chickadees, and sleeker. During the winter, the male's bright, lemon yellow plumage is exchanged for olive drab. The distinctive black wing bars are still distinguishable. The female of the species is a tan color, with less obvious markings.
Scarlet Tanagers winter in the tropical forests of Northwest South America, and make a nocturnal migration to the northern U.S. Males are a bright red with black wings; females are similar in color to the American Goldfinch, but much larger (approx. 7" in length).
Although their numbers have decreased precipitously over the past few decades, you can still catch the occasional Eastern Bluebird at your feeder if you are tenacious. The male has a wonderful sky blue black and a russet chest not unlike the color of a male robin. Bluebirds are quite a bit smaller, though. Female Eastern Bluebirds have similar coloring on the chest, but their backs are a dull gray with blue edging the wings and the top of the head.
The male Indigo Bunting is one of the most striking birds that will ever visit your feeder. Approximately 4.5" long, the male is a brilliant blue. The female is a dark, dull brown. The Bunting's diet is primarly insects, but it can be lured with a fruit/seed mixture and it prefers feeders with a perch.