The first recommended website is that of Stargazers Lounge, which, at the time of writing has over 23,000 members worldwide, and is rapidly becoming the world’s leading online resource for Astronomy. If your not a member already, I would recommend signing up as soon as possible.
Stargazers Lounge
Online astronomy forum of International repute
First Light Optics
Suppliers of astronomical telescopes, binoculars and accessories.
Starlight Xpress
cost-effective cooled CCD cameras and accessories for astronomy
Ian King Imaging
CCD cameras, telescopes and accessories
Modern Astronomy
For visual, video and CCD astronomy
Baader Planetarium
Photographic CCD filters and other accessories
Astronomik
Photographic CCD filters
Websites created by some very good friends and colleagues, many of who are regular contributors to the mainstream astronomy magazines.
Steve Loughran
steves-astro
Martin Bradley
astropixels
Mike Deegan
Mike’s Astroimaging
Harry Page
Harry’s Astro Shed