There are many websites offering online records, but the one that stands out above the rest is TheGenealogist. This is a vast online research site, holding complete BMD and census records, along with Parish Registers, military records, directories, non-conformist records, and much more.
Parish records are available in two formats - transcripts/database records and searchable printed books. The database records consist of easily searched transcripts of the original records which allow you to search on various fields and may also have linked images of the original registers. The searchable books consist of indexed books that were transcribed and published many years ago, many over 110 years old. These transcript books have then been OCR'd (Optical Character Recognition) to turn the pages into searchable text.