Jewishism or something? No frickin’ idea.
There’s a bunch of people around here insisting atheism is a religion, so I’ll choose that one.
I have a soft spot for Sikhism
This. And from what I’ve heard, half of them are atheists anyway.
UU would be my first choice too. If that’s forbidden on the basis that you don’t really have to believe in God to be UU, then I guess Anglican. It’s what I grew up with - although my parents were (and are) atheists, the rest of my family are Anglican, and I went to an Anglican school, so I know the drill. And as religion goes, Anglicanism is pretty inoffensive, and it has nice language and rituals at least. (The local diocese is very High Church.)
And hey, it would make my grandmother very happy, I guess. 
I’d be a Catholic. My extremely limited understanding of Catholicism leads me to believe you could actually murder the Pope and after expressing remorse through confession and undergoing some ritual penance be forgiven, possibly even by his successor and get a pass through the pearly gates.
Some benevolent cult where I get to have sex with lots of willing nubile women.
hellenic polytheism
Keep practicing the conservative/Reconstructionist Judaism I already do.
Taoism
Pastafarianism
I consider myself an atheist and a Discordian.
I might go for whatever that half-snake puppet thing is that Alan Moore seems to like.
Is he anything likeJake the Truth Snake?
If I had to pick a religion, I might go back to being Roman Catholic. Yes, I’d have arguments about some Church policies–but they haven’t burned anybody in years!
Although I doubt that Buddhism is all that Theist. And I’ve had a liking for the Discordians since finding their screeds among the piles of “serious” pamphlets at Houston’s defunct New-Agey Phoenix Books.
I’d just go back to Hinduism. I never really left it. Why change?
I like this one
Just saying 
I’d probably go back to (Norse) paganism. I still sort of consider myself a “pagan atheist”, actually.
Animism sounds appealing, too. I already argue with inanimate objects enough.
The scary kind of devil worshipper that they used to talk about in the 80’s on Geraldo.
Yes, the nice thing about Judaism is that you don’t have to choose. 
Ditto this (substitute Reform Judaism, although I really wish the Reconstructionist movement had a bigger presence in the UK).
I guess I’ll be the one to take this in a different direction. I’m still trying come up with something, anything, that would cause me to feel I had to choose a religion, and also wrap my mind around the illogic of choosing what to believe in.