Inspired by the "where'd all the birds go?" post, here's some links that are good for finding out where they went!
http://www.birdingonthe.net/ (click the regional/speciality link at the top for links to statewide birding list serves)
Ebird:
http://ebird.org/content/ebird/ - check out the View and Explore Data function. For example, here's a bar chart of frequency of occurence for species at the location I will be birding sunday - Andrew's Point at Cape Ann, MA:
http://tinyurl.com/ycux7gg It tells me I have a good chance for my main target birds: Harlequin Duck, Dovekie and Thick-billed Murre, among other good coastal species.
There's also the eBird google map of sightings:
http://birdingonthe.net/gmaps/eBirdMap.htmland if you want to know about really rare birds that pop up in North America, check out PEEPS:
http://birding.typepad.com/peeps/Good birding!