I play with 3-week seasons (a mod gives that option) and have at least 1 holiday per week. I also use a mod that adds some additional holiday traditions to help round them out. Each season has at least 3 holidays. Spring and Winter have 4, and I don't have all of them tagged to be an off-work-day... unless vacation is used, of course (designated by asterisks in my list).
The Holidays I have set up, in order, are:
Spring:
- Spring Has Sprung - at the start of spring, basically just a spring cleaning holiday with Cleaning and gardening being the holiday traditions.
- Day of Famine* - Friday before Easter, with Attend Ceremony, Fasting and Decorate as the traditions.
- Springfest - Basically Easter Sunday, with Decorate, Egg Hunt, Flower Bunny, Grand Meal, and invite guests traditions.
- Day of Song - A day to celebrate the arts, with Art & Music Spirit, Decorate and BBQ traditions. From the mod, I also have Art Exhibition and Go to a Music Concert traditions here.
Summer:
- Llama day - 4th of July/Independence day for the sims. Decorate, Drinking, Fireworks, BBQ and Water Fun traditions
- Summerfest* - I'm from the Milwaukee area of Wisconsin, this emulates a concert event that happens there. Traditions are Drinking and Go to a Music Concert
- Day of Remembrance - Tell Stories, Remembrance, Fire, Go on a Vacation/Travel traditions. Also from the mod, Hiking Trip tradition. -- sorta my mother's day, father day, memorial day all rolled into one.
Fall:
- Oktoberfest - BBQ, Gardening, Drinking, Party Spirit, Holiday gnomes traditions.
- Spooky Day - Wear Costumes, Trick or Treat, Spooky Spirit, Decorate and Mischief Spirit traditions.
- Harvestfest (basically Thanksgiving) - Thankful Spirit, Sports TV, Decorate, Grand Meal, Invite Guests
Winter:
- Polar Plunge* - Again..from wisconsin, so I had to have this in there. Polar Bear Plunge and Drinking as traditions.
- Winterfest Eve - Give Gifts, Father Winter, Decorate, Baking, Attend Holiday Ceremony traditions
- Winterfest - Festive Lighting, Decorate, Festive Spirit, Open Presents, Grand Meal
- New Years Eve - Party Spirit, Make Resolutions, Decorate, Drinking, Countdown to Midnight
- Love Day - Watch Romantic TV, Romantic Spirit, Go on a Date, Give Flowers, Decorate
Been through one full year cycle so far since setting them up and things have been nice. Frequent enough holidays to enjoy them, but enough days in between to lead a normal sim life most of the time.