A government backed site that has information on state pensions, workplace pensions and personal pensions:
http://www.pensionsadvisoryservice.org.uk
For information on state pensions and retirement planning, including getting a state pension forecast:
http://www.gov.uk
A website that provides advice on options for using a pension pot:
http://www.pensionwise.gov.uk
A useful website for advice on pensions and retirement planning:
http://www.themoneyadviceservice.org.uk/en
Two websites with many useful resources regarding pension planning:
http://www.hl.co.uk and http://www.pensioncalculator.org