Rare Bird Network – a free bird sightings network for the UK primarily aimed at Twitter users. It is for both UK and local rarities, the website gives the full information as to how to make the best use of the service.
Surfbirds – a British/USA collaboration featuring the best birding articles from both sides of the Atlantic, including rarity news, predictions, mystery photos...great site.
Virtual Birder – a fantastic site with virtual bird walks around North American sites. At the moment it includes a trip round Cape May. You can take the virtual tour and identify the birds that you see as you go round, accumulating points and attempting to beat the high scores. There is also a lot of information about birding in North America.
Met Office – the first port of call if you are after weather information and forecasts in the UK and all around the world.
Wetterzentrale Top Karten – Georg Mueller's amazing site crammed full of charts from nearly all of the world's meteorological organisations. Some knowledge of German useful, the Google translate function is also helpful here.
National hurricane center – where is that hurricane heading? Will it bring those transatlantic rarities with it? Find out its predicted path here.
BBC weather – another site providing much of the same information as the Met Office site but in a different format.