This is one of the best genealogy sites you can get on the internet. It is a treasure trove of information if you are searching for your ancestors. The main features are the UK census
Collection from 1851 to 1901 also the UK birth marriage and death index records from 1837 to 2000. The pallot marriage index and UK parish and probate records. Plus loads more.
UK census records

At the moment the records available to us are from 1851 to 1901 there is talk that the 1841 will be available by the summer 2006 .very easy to use enter all the information
You have on an ancestor: name- date of birth-place of birth and the site will come up with two options exact match or ranked match .Once you have found who you believe to be your ancestor. You can read the census image it will give you an address occupation and the family who resides at the address. Using the census you can trace your family back to before 1800s.you can also use it to find out what their partners names were and any children they had.

The B.M.D. Index

This is a list of all births marriages and death registrations from 1837 to 2000.
It is listed by name year quarter volume and page number. The year is divided into 4 quarters march-June-September-December ie March quarter would contain January -
February-march.

The birth index

From 1837 to 1912 you will find the surname Christian name district of registration volume and page number from 1912 onwards it also gives the mothers maiden name.

The marriage index

This list all marriages from 1837 to 2000 it is basically the same as the birth index ie,
Year, quarter, registration district name volume and page number.
From 1837 to 1911 only one partner is entered after 1911 both partners are entered.

The death index

Same as previous two ie; year; quarter and so on but the age of death is entered making it
Easier to cross reference with date of birth.
These indexes do not give any information such as address parents or actual event dates
But you can use them to order any of the above certificates from the G. R.O. using the
Reference numbers ie; volume and page numbers not forgetting that there is a charge for
Any certificates ordered from the G.R.O.
Pallots marriage index

This is mainly used by people searching for marriages in and around the London area.
The dates are from 1780 to 1837.All records are hand written and identifies the church
Names of the couple marrying and the date .there are a few counties this also covers.

UK parish and probate records

These records were collected by the church and each parish it governed. Records include
Birth; baptism /christening; marriage and death .These are useful for information before
Civil registration came into being in 1837 .You usually find that a family stayed in one area and used the same church for all family events therefore you could be lucky and find
Your family going back several generations.
There is also an online family tree builder which is easy to use and store all your old and new information in. Also there are message boards.
Ancestry.co.uk
has several different subscription packages and I believe this site is worth every penny.