Here are some basic ones to start you off....
Family Search site- LDS -very good site for parish registers-Online birth, marriage, death, census, church and other indexes.
Uk bmd -This site provides 1204 links to web sites that offer on-line transcriptions of UK births, marriages, deaths and censuses
Free BMD site - for civil registration GRO refs
Ancestry - census and many other useful records
For more links see our Useful Links sections