^{A Good place to start is the Science course available from the Guardian Web Site:
Most of the sections can be accessed as follows:}
http://www.guardian.co.uk/theguardian/2008/apr/26/sciencecourse
The Universe
http://www.guardian.co.uk/theguardian/2008/apr/28/sciencecourse
The Earth
http://www.guardian.co.uk/theguardian/2008/apr/29/sciencecourse
Humans
http://www.guardian.co.uk/theguardian/2008/apr/30/sciencecourse
Energy
http://www.guardian.co.uk/theguardian/2008/may/01/sciencecourse
Building Blocks
http://www.guardian.co.uk/theguardian/2008/may/02/sciencecourse
Experiments for Kids

But Section 2 can only be accessed as the individual papers:

http://www.guardian.co.uk/science/2008/apr/27/genetics.evolution
What Is Life?
http://www.guardian.co.uk/science/2008/apr/27/genetics.fossils
Wiped Out
http://www.guardian.co.uk/science/2008/apr/27/genetics.darwinbicentenary
Evolution and Darwin
http://www.guardian.co.uk/science/2008/apr/27/genetics.evolution1
Life On The Edge
http://www.guardian.co.uk/science/2008/apr/27/infectiousdiseases.stemcells
Can We Create Life?
http://www.guardian.co.uk/science/2008/apr/27/genetics.cancer
What DNA Can Tell Us
http://www.guardian.co.uk/science/2008/apr/27/genetics.plants
A Delicate Balance
http://www.guardian.co.uk/science/2008/apr/27/genetics.biochemistrymolecularbiology2
What is DNA?
http://www.guardian.co.uk/science/2008/apr/27/medicalresearch.genetics
What Happens When Genes Go Wrong
http://www.guardian.co.uk/science/2008/apr/27/genetics.biochemistrymolecularbiology
The Library Of Life
http://www.guardian.co.uk/science/2008/apr/27/genetics.biodiversity
The Actual and the Possible

Included here are a very few key websites chosen from thousands of Science sites on the Internet.

UNITS If you get as confused about pascals, newtons, etc. as I do, have a look here.

PHYSICS  A-Level Physics covers most of classical physics.
                  The ABC's of Nuclear Science covers, at an elementary level, the main topics of nuclear physics.

 INORGANIC CHEMISTRY covers most areas of inorganic chemistry.

LIFE CHEMISTRY  the Life Chemistry paper in the Universe Story topic includes some good links.

BIOLOGY  TEXTBOOK covers most aspects of biology at a level suitable for the general reader.
Also try Kimball's Biology Pages for a very wide-ranging site.
This is a comprehensive account of biological evolution.

EARTH SCIENCES a very wide range of materials
But also have a look at
           Geology – UCMP Exhibit and West's Geology Resources are worth looking at if only for the
             County Maps
           METEOROLOGY a good introduction to the subject.
           The Remarkable Ocean World

ASTRONOMY There is a rather nice digital orrery  and a comprehensive history site 

And of course there is always wikipedia