ATS is a great site which i use very often however i think it would be a great idea for people to post links to alternative forums which are related to science, space and paranoramal/conspiracy etc.
I will get it started:

www.unknowncountry.com... Like ATS.

www.paranormalnews.com... Like ATS.

www.bvalphaserver.com... Another like ATS.

www.darkgovernment.com... Similiar to ATS again.

www.focusmag.co.uk... Science etc.

www.exn.ca... Science etc.

www.thespacesite.com... Space+science

www.universetoday.com... Space+science

www.scienceforums.net... Pure science.

www.space-talk.com... Space.

Well that will do for now, please share your sites as it will be a benefit to the whole ATS community