Stellarium - a fantastic and beautiful planetarium for your PC - awesome and free !
StarGazers Lounge - the most useful and comprehensive forum for anything to do with Astronomy - a great bunch of friendly and helpful people.
UKAI - United Kingdom Astro Imaging forum - UK biased but very friendly and helpful people
Aurora watch - the best site for showing when Aurora is likely to be visible
Live Aurora - see the Aurora live !
Whats in the sky tonight - enter your location and it will tell you what you can see
UK Astronomy Buy and Sell - THE place for buying and selling anything to do with astronomy
APOD - Astronomy Photograph of the day - changes every day - some amazing images !
Clear Outside - Weather forecast for Astronomy
Ventusky - excellent general weather forecasting
Pixinsight - the Gold Standard for Imaging
Stellarium - a fantastic planetarium for your PC - awesome and free !
Stellarium Scope - this is an add on to the above programme - just click on the object you want and this add on will point your scope at it
PHD2 - free guiding programme
Astrotortilla - plate-solving software to make sure your scope is pointing where you 'think' its pointing
APT - Astro Photography Tool - computer control over your camera, filter wheel and imaging plans etc
EQMOD - the software that makes all of the above talk to each other and work in harmony - I can't believe that this is FREE!
FocusMax - computer control over your focuser
Astrometry - plate solving service - free.