The first nonbeliever I can remember from TV--Michael Stivic from still my favorite sitcom ever, All in the Family.

None when I was growing up (that was too long ago) but I can still remember how I nearly swallowed my tongue when the security chief on Babylon 5 casually revealed that he was an atheist. And I was in my 40s at the time.

Dave Allen (UK tv) He'd always finish his show with "May your god be with you"

Two of my favorites - watched all of their shows. Also Bill Maher.

We all have forgotten a big one Bill Maher

Gilligan, the Skipper made him read the bible every day before he had his coconut milk.

I've seen several references here to the original Star Trek series, but it wasn't quite as atheistic or agnostic as people remember. In particular, in the episode "Who Mourns for Adonis," the crew meets Apollo (a powerful alien being, but the same entity from Greek antiquity) who captures them and wants their worship. This exchange takes place:

APOLLO: But you're of the same nature. I could sweep you out of existence with a wave of my hand and bring you back again. I can give life or death. What else does mankind demand of its gods?
KIRK: Mankind has no need for gods. We find the one quite adequate. [emphasis mine]

I suspect Kirk's qualifier was tossed in to appease audiences, and the studio, as being too obvious about atheism in 1967 was probably bad for viewership. Today's sci-fi audience is pretty accepting, I think, but 50 years ago it was a different matter. For the most part, they just didn't reference religion or theistic views at all.

Karl Marx, nothing is more real than Real Life, otherwise is... made up.

There was a very long running local variety/comedy show in AZ called the Wallace and Ladmo show. As far as I remember they never took any stance either for or against religion.

They were pretty irreverent. I well remember Pat McMahon dressed in drag as Aunt Maud in one of his many character roles hitting on the local cop doing PSAs for the show. It turned into a running joke with the cop horribly embarrassed every time he came on. Ha, ha.

RCC Edit: Since @LiterateHiker mentioned Fractured Fairy Tales. W&L also often featured a lot of cartoons aimed as much at adults as children. Fractured Fairy Tales, Roger Ramjet, Super Chicken, George of the Jungle and others were some of my favorites. Thanks for the reminder.

Red Foxx, from Sanford and Son and Carl Sagan.

It is a sticky wicket to have non believers on TV figure how it was to get gay people out in the open

Star Trek. The original series. All the civilizations evolved past all that.

superman

As a Brit, I can remember Terry Wogan on telly all the time when I was younger. I always thought he was an Irish Catholic, and nominally he was. However, in an interview on BBC a few years before he died he disclosed that he no longer believed there was a god. I always liked him anyway, but he rose several notches in my eyes then.