I guess another good criterion here to add is that the holiday is NOT commerical in nature.  That would then eliminate the Super Bowl.  Labor Day is another good add.

What I can say I see, when you have people trying to actively come up with something specifically not religious, is the holiday in question (or some other cultural artifact) ends up being the cultural product of a nerd.  Not sure nerd culture stuff will have mass approval.  On the language side, you get Esperanto and Klingon.  Festivus is one on the holiday side.  You have other stuff like the Jedi religion.  Stuff ends up being too brainy for its own good.  As someone did mention Pi Day is another, and that would also fit as "Too Nerdy".  Like Darwin day, it ends up being a trumpeting of intellect.  It reminds me of the top 50 atheist lists.  It is generally about intellect.

There is Kwanzaa, which is the creation of a Marxist college professor, so that might count.

so just like an atheist.

It is a trend I am seeing, and I welcome counterpoints to this.  Like, what gets heralded as top atheist lists:

http://www.superscholar.org/features/influential-atheists/

It is all about intellect above everything else.  You see other religious side, and people will herald moral character.  It is just the atheist side, it seems to be all about intellect.  Individuals with spotty personal lives get heralded as being great.  

And here is another one:

http://www.thebestschools.org/blog/2011/12/01/50-top-atheists-in-the-world-today/

Contrast that with how other people end up doing top list:

http://content.time.com/time/specials/packages/article/0,28804,2111975_2111976,00.html

http://www.adherents.com/adh_influ.html

You do understand that those holidays are there, because they were chosen to be there. It's not like Jesus was actually born on Christmas, but it is put there as a day of rememberance and if an astronomical even is there or not makes no difference. The fact is the majority of the people celebrate Christmas not the winter solstice, lol.

The easter we know is becasue of Jesus rising from the dead, not because of a celebration of sex and fertility, that was added back later. And even though a lot of Athiests try to hide the Easter that most people celebrate, again most people aren't celebrating ishtar.

Just trying to give you my input.

the only counter point i can think is atheists are a diverse group so no one particular statement may apply to all of them.

the "religous" athiests i know tend to have something of a similar backstory of not being able to have faith in an idea (religion) that has no evidence, proof, or substantive argument beyond "believe or you will be punished for not believing".  and that tends to be the same skepticive outlook that is the foundation of scientific thought.  so yeah, many atheists are intellectuals that pride intelligence over other personal attributes.

..but there are also the apethetic athiests that don't believe in religion not because they are adamant religion is wrong but they don't care to learn enough out religion to disbute it.  ..and then there is the agnostic athiests.

You are missing the kind of atheist I see the most oddly.   The "Brought up Evangelical or strict Catholic Atheist."

They're always fun because while they rail against everything they were tought, they never really pick up critical reasoning skills so they tend to support any silly ass theory that is a counter to organized religion.

These are the people that believe in stuff like Zeitgeist and there being no historical christ.

Essentially not focusing on the intellectual or the moral, but instead simply reflecting against what they were previously taught.

Pi day's a favorite of mine.

Halloween is also fun, but I guess it kinda has theistic origins, even if not monotheistic....

oh yes, that's another good one!  i'll dub them the rebellion atheists whom are more obsessed with discrediting religious ideas then they are with substantiaing their own ideas.  they tend to be obsessed with things like pedophillia in the church and anything else that can help vilify religion.  ..the sterotypical "angry" atheist.

There may be some exceptions, but my view is that when people deconvert from something, unless there is some other element that drives change outside the person, the person will remain the same, but have a different view.  In short, if you were a really obnoxous religious person, you become a really obnoxous religious person.  Dan Barker, for example, stopped being an evangelical Christian, and went on to be an evangelical atheist, founding an organization to promote lack of religion.  Same person, just without the Christian religion.

I can say someone can deconvert and take a more humble view of things, but that isn't that common.  Or at least such a person really isn't heard from afterwards.

You mean Apollo's Day!  Apollo being the Greek Sun God riding in his chariot.  Hince Sun day, day for worshiping the Sun.

The Christian Holy day is actually the same as the Jewish one, Sundown Friday to Sundown Saturday, but it was moved by Emperor Constantine so that it would fit bet into the current religions of Rome and cultures.  The 7th Day Adventist and a few others still worship that day.

So still a religious base.