Well, that was an amazing chunk of information from s_anthony! There were a few things in there that I was not aware of, but I would like to add just a couple of things.
Just after Rosh Hashanah, comes Yom Kippur. This is the most solemn day of the Jewish calendar. It is not a holiday to send cards, but we fast from sun up to sun down. Most Jews spend most of the day in synagogue. We pray to be written in the book of life for another year (hence the proximity to Rosh Hashanah.) I just felt it needed to be mentioned.
The one that I always got a kick out of was Succos (or Sukkot). (The synagogue I grew up in said bas mitzvah, not bat mitzvah.) It is a harvest holiday, and you build a succah in the back yard. My dad did one a couple of years using some wooden framework. Then we bought cornstalks and tied them to the wood. We used gourds, indian corn, etc. to decorate. I remember it being a fun holiday, so a traditional fall card just mentioning the holiday might be appropriate.
Just one more thing that I would add: I wish that SU would do a Chanukah set spelling it with the ch. That really is the correct pronounciation of it. (Remember the Rugrats special that said "Chanukah....you have to ch when you say it.) FYI, that ch is not pronounced like in the word church. It is a gutteral sound in the back of the throat. Many people who weren't raised with the sound cannot even do it - just as I can't roll an R. Anyway, I would love another Chanukah set, spelled that way!
I would also add that most Jewish people are not offended if you say Merry Christmas to them. When I check out in a store and the cashier says "Merry Christmas", I say thank you and answer "Merry Christmas to you too." I don't feel compelled to say "Happy Holidays", and I am born and raised Jewish (though married to a Catholic). (We've been married 21 years now, so I think it worked out okay.) I love sending Christmas cards to my friends, but I stay away from religious themes. There are so many other choices, I can wish them a Merry Christmas with snow or Santa, etc. I am not offended if my friends send me a card that says Merry Christmas either. I know that it just means that they are thinking of me. One year, a coworker sent a card to everyone but me, trying not to offend, but that made me sad. I would rather be included in the good wishes!
I do make a point of making and sending Chanukah cards to relatives.
Well, I've rambled.