Voltage Level Standards

The commonly used level standards are:
TTL | CMOS | LVTTL | LVCMOS | ECL | PECL | LVPECL | RS232 | RS485 | etc.

as well as some relatively high speed:
LVDS | GTL | PGTL | CML | HSTL | SSTL |etc.

Also,
Lower Voltage LVTTL (not commonly used; mostly in high-speed chips)