Apart from the ones mentioned GrandPrix.com is worth a read. You should also check out the teams official sites, they often release news long before the major news sites show them – but this is only good when you really have nothing to do, otherwise it’s too time consuming!
I pretty much use NewsNow all the time for all the news not just F1. The above link will take you to the F1 news site but on the left side you can select any category you want.