eBird is a website for the serious birder. Created by the Cornell Lab of Ornithology and the National Audubon Society, the site builds a database of bird sightings based on the observations of recreational birders.
From the website: "Every time that you see and identify a bird, you are holding a piece of a puzzle. Whether you are casually watching birds in your backyard, or chasing rare species across the country, you are helping to put this puzzle together."
There is a straightforward tutorial on the site here.
Whereever you've seen your birds, you can upload the location, date and species that you observed. The data is collected and can be accessed via graphs, charts and other tools.