One of the best sources on the occurance of rare birds is the birding hotline. The following information covers two national rare bird alert systems and a listing of many regional and state birding hotlines. It is a group of mirrored mail lists run from a listserver at Arizona.
Users subscribe to the lists, and mail files sent to the list are reflected back to all subscribers.
Some lists are for general birding and bird-related discussions, and some are specifically for posting RBAs and hotline transcriptions. Other sources were used to a lesser extent. Daan Sandee also posts a listing of bird hotlines. Please e-mail any adds or changes and the list will be updated.