One of my favourite free genealogy resources is FreeBMD. It's an on-going project in which the birth, marriage and death indexes of England & Wales are being transcribed. While the whole index hasn't yet been transcribed, there is still a lot of information there, especially pre-1930.
You can search for all types or just birth, marriage or death, along with surname and/or first name. Other details such as spouse or mother's surname, along with date range and district or county can be included in your search information (the more information you put, the more relevent the result should be... although sometimes you need to only put a little information... It needs to be remembered that because the indexes are being transcribed human errors can occurr (and there may have been an error in the index anyway).
The results you are supplied with will give you the details with which (assuming you think you may have found the right person) you can go to the GRO (General Register Office) with and apply for the relevent certificate.
Over the years, I have found FreeBMD very useful... You can even select the district name and type in the volume & page to see who else was on that page of the register... Very useful if you suspect a twin or to see who else was married in the quarter.
Pickards Pink Pages for Warwickshire England are really interesting free website for people with ancestors from that county.
Volunteers are encouraged to submit extracts from PRs and there is also a section where people can list their interests. Pickard charges nothing for the service he provides. Well worth a look.
Also free is Northamptonshire Stray Marriages website, again anyone finding an out of county marriage is encouraged to add to the index, invaluable for the bride or groom marrying away from their home county.