Off the top of my head there are:
Cylinder via general HP
Cylinder with dedicated DHW HP
Cylinder via immersion only
Sunamp models and similar
Tepeo models, particularly ZEB
Electric instant hot water centrally
Electric instant hot water at point of use
Solar thermal (which I have in addition to my HP)
Geothermal (but not in the UK)
(Anyone got more suggestions?)
Edit:
Other electric boilers (not Tepeo or similar)
Direct PV to immersion heater