The Sky at Night pages from the BBC, associated with the long-running TV programme of the same name.
Heavens-Above - Mainly concerned with artificial satellites, but also offers sun, moon and planet data for your location.
Visit the SpaceWeather site to keep up to date with what is happening to the sun, and for auroral predictions.
After months of declared intention to de-orbit the Iridium satellites, the Iridium constellation continued to be maintained and was finally reprieved, and Iridium Flares gave a brilliant introduction to sky watching - details for your location could be found at Heavens-Above. The more recent Iridium Next satellites do not flare in the same way. I have summarised the Iridium Constellation Status.
The Visual Satellite Observer's Home Page
SeeSat-L Home Page - the mailing list for visual satellite observers
Well, the sun and moon are responsible for the tides!
Predictions for the Severn Bore and Trent Aegir are now on the Environment Agency site.