FreeREG: searches of baptism, marriage and burial records in parish and non-conformist church registers in England.
Free BMD: free search of English Birth, Marriage and Death indexes on-line (transcribing is on-going and far from complete).
Family Records Homepage: used to be a subpage of the PRO website (England & Wales); offers more information on Civil Registration, Wills, Parish Registers, India Office Records, Welsh Registers, etc.
English Origins: pay to use but free surname search of several collections held by the Society of Genealogists (England); more collections to be added throughout the year.
Scots Origins: pay to use; includes all the Civil Registration indexes for Scotland (starting 1855) and the old Parish Registers index, all held at the Scottish Record office; also links to "Scots Life," etc.
Informational Leaflets from the Public Record Office: many different printable and/or downloadable leaflets.