I guess I would have to say My Birthday, Christmas Day. We also like Halloween, F & W, Flower Time at Epcot. There is just too many, I guess we just need to stay around all year....
And I guess it is not technically an event but anytime you can celebrate a birthday there it is great. I haven't had the chance yet but have taken a friend for her 40th and some family members for their birthdays.
We like Mickey's Not So Scary Halloween Party, not so many people in the park, we're able to get on most of our favorite rides many times, you get so much candy and you get to see the Headless Horseman ride through, but WOW sure can be expensive.