ASKE- Association for Skeptical Enquiry.
Arse Biscuits!- A site looking at nonsense.
British Humanist Association- supporting and representing the non-religious and campaigning for a secular society.
ebm-first - A look at alternative medicine and its issues.
The Richard Dawkins Foundation for Reason and Science
The 21^st floor
Tony Youens - Prominent UK skeptic.
The Quackery page - by Professor David Colquhoun
Tomorrow is here - for science and technology

International sites of interest:

Quackwatch - Guide to Quackery, Health Fraud, and Intelligent Decisions.
The Skeptic's dictionary. - This is more like an encyclopedia - a great resource.
The Skeptics Society - Michael Shermer's Skeptics Society.
CSI - Committee for Scientific Investigation.
Indian skeptics.
Skeptical science. - A (proper) skeptical site examining so-called "Global Warming Skepticism".
The two percent company. - A site offering a rational outlook on things.
Snopes. - An excellent site looking at urban legends. Many "true" anecdotes and Friend Of A Friend (FOAF) stories are nothing more than urban legends.
Reitstoen - A great multimedia archive.

Blogs:

The Skeptic - Latest news.
Skeptico - Critical thinking for an irrational world.
Garvarn's blog - Thoughts on Superstition, Pseudoscience, and the Paranormal
The skeptics circle
A sceptical I
The Hampshire Skeptics Society
Random tangent - Australian blogger
Jerome's blog - CJ's weblog: the idle thoughts of an idle fellow
Place of Stuff

Publications:

Skeptics' magazines well worth subscribing to.

UK:

The Skeptic - edited by Professor Chris French.
Now or Never magazine

USA:

Skeptical Inquirer - the magazine published by CSI.
Skeptic - published by the skeptics society in the USA.

Paranormal investigators:

Hayley Stevens - Hayley is rapidly becoming a voice of reason in the often irrational, assumption led world of 'ghost hunting'.