FamilySearch is the biggest and best-known site for parish register indexes, but it isn't the only one.
A number of English counties have Online Parish Clerks, volunteer transcribers who 'adopt' parishes and put the results online, free of charge.
They are all works in progress, but worth a look if your county of interest is listed here.
The Online Parish Clerks have are separate sites for each county, but another site worth searching is FREEREG, which includes transcriptions from many counties in England, Wales and Scotland.
Many printed parish register transcripts can be downloaded from The Internet Archive including publications by Phillimore and Co, and some parish register societies.
Better yet are free digitised images of parish registers, and you will find these for some parishes in Kent and Essex. They are not indexed, although you may find indexes elsewhere, such as on FamilySearch or Online Parish Clerks. History House - dip into the history of Essex links to digitised images of some parish registers in the Essex Record Office. Registers from the area round the Medway Towns in Kent are on the Medway Archives CityArk site. This is not the most user-friendly site I have ever used, to say the least, but given the choice, I'll take inconvenient but content-rich over pretty but empty every time! For anyone not familiar with the term 'Medway Towns', it is the area round Rochester and Chatham; Chatham includes not only Chatham Royal Naval Dockyard, but is also a garrison town, so it is interesting for anyone with ancestors in the Army, Navy and Royal Marines, who may have been stationed there at some time. The Mid-Kent Marriage Index 1754-1911 is a useful resource for another part of the county.