Here in suburban Maryland, the list is long. There are the well known cardinals, chickadees and blue jays, as well as titmice, goldfinches, house finches, white breasted nuthatch, downy woodpecker, chipping sparrow and more.
While species interaction might mostly consist of shoving each other off the feeding perches, others may include the passing off of seed or bits of suet from one mate to another. Sometimes a displays ensue, like wing flashing and body shivering, with special calls reserved just for the mate.
If you're looking to identify a bird you might not recognise you might find Audubon's app useful, or visit Cornell's All About Birds sight and search their bird guide.
Overall, this is a very rewarding endeavor, especially when you can sit near a window or out on your porch and get closer to the birds than you might ever otherwise. So try it out! Oh and be sure to get a squirrel-proof feeder if you don't want to have to keep refilling your feeder every couple days. Check out your local wild bird store for squirrel feeding options.
Enjoy!