Whether or not you consider yourself an experienced birdwatcher, you're likely to find free web service eBird a great resource for all kinds of data, including frequency, abundance, counts and locations for tons of different species.
eBird, along with help from their partnerships around the world, has amassed a pretty large amount of data, all organised in a way that's super easy to understand. You can view statistics of up to five species at once as graphs, histograms, tables and maps, which you can filter down further by geographic location. You can even save certain tables you want to keep track of instead of returning to the site over and over again.
If you are an experienced bird enthusiast, you can even contribute data you collect to the site using pre-constructed forms — whether it be just observing counts or results from actual experiments. If you register with the site, you can also get alerts sent to you about important events, so you don't have to keep track of it all yourself. And, of course, it's all free. Check out the site for more details.
eBird [via MakeUseOf]