A great thing to do if you feed backyard birds is maintain a "Life List." This is simply a list of species you see at your feeder or in your yard, with the location and date you first spotted it.
As you continue feeding birds, a Life List will be a great help in remembering if you've seen a particular bird before, what time of year certain species appear, and when you saw a rare species.
It is also a great activity to do with kids. Letting them help maintain a Life List will give them a sense of involvement, and will be the basis for some great memories as they get older.
We've been maintaining a Life List for several years, at two different houses, and it has been educational as well as a lot of fun to go back through it periodically.
You can make your own life list, and many bird field guides have a Life List section in the back where you can check off species that you've identified.