Here are my favorite shows in this genre for each letter of the alphabet:

0-9 – The 4400 (2004–2007)

A – The Adventures of Brisco County, Jr. (1993-1994)

B – Babylon 5 (1993-1998)

C – Courage the Cowardly Dog (1999-2002)

D – Doctor Who (1963-1989, 2005-present)

E – Eureka (2006-2012)

F – Firefly (2002)

G – Get Smart (1965-1970)

H – Hitchhikers Guide To The Galaxy (1981)

I – Inspector Gadget (1983-1986)

J – The Jetsons (1962-1963, 1985, 1987)

K – Kolchak: The Night Stalker (1974-1975)

L – Locke & Key (2020-present)

M – My Favorite Martian (1963-1966)

N – Night Gallery (1970-1973)

O – Once Upon a Time (2011-2018)

P – Primeval (2007-2009, 2011)

Q – Quantum Leap (1989-1993)

R – Red Dwarf (1988-1999)

S – Sliders (1995-2000)

T – The Twilight Zone (1959-1964)

U – The Umbrella Academy (2019-present)

V – Van Helsing (2016-2021)

W – Westworld (2016-present)

X – The X-Files (1993-2002)

Y –

Z –