The following are sources of reference or information for family lawyers on the internet. Please note that I have no control over these external sites and cannot therefore accept any responsibility for their contents.

Statutes:
The UK Statute Law Database - contains (mostly) updated Statutes and Statutory Instruments.
Office of Public Sector Information - includes UK legislation since 1987.

Cases:
British and Irish Legal information Institute (BAILII) - British and Irish case law & legislation.
Family Law Week - judgments of family cases since 2005 (some pre-2005).
House of Lords judgments - delivered since 14 November 1996.

Courts:
HMCS - includes court locations, forms and advice.
Family Proceedings Rules
Civil Procedure Rules
Judiciary of England and Wales

News:
Family Law NewsWatch - news and articles in Jordans Family Law periodical.
Family Law Week - excellent site full of news, cases and articles for family lawyers.

Groups:
Resolution - if you're a family lawyer and not a member, why not? Site includes information, press releases and section for members.
Family Law Bar Association

Ancillary Relief:
Pre-Application Protocol
Ask.com share prices
Retail prices index
Companies House
CGT Indexation Allowance
Currency Converter
HM Land Registry
Salary Calculator

Child Support:
Child Support Agency Advisers section - includes procedural guides.
Child Support Commissioners' Decisions.

Children:
National Association of Child Contact Centres
CAFCASS

Mediation:
National Family Mediation - network of local not-for-profit Family Mediation Services.
UK College of Family Mediators

Child Abduction:
Foreign & Commonwealth Office
Hague Conference on Private International Law - includes list of member states.
Reunite - charity specialising in international parental child abduction.

Domestic Violence:
Women's Aid

Taxation:
HM Revenue and Customs

Benefits:
Department for Work and Pensions

Professional Bodies:
The Law Society
The Bar Council
Solicitors Regulation Authority

General:
Delia Venables Legal Resources - huge source of information for individuals and lawyers.

I will be updating this list from time to time. If you have any suggestions for inclusion, or find any broken links, please let me know by commenting below.