Fall is a fantastic time for festivals in Budapest. Some of the biggest and best events happen during harvest time. The Budapest International Wine Festival in mid-September grows more and more popular every year. Its Wine University is a great way to learn about the beverage and wine culture. There's also a parade and plenty of good food. If you're after good food...just wait until October for the Budapest Pálinka and Sausage Festival held at the Buda Castle. What's your favorite???
I second the Budapest Wine Festival. It's one of the biggest and most popular events of the year, though you really have to like your wine to enjoy it. Another event I recommend is the Chocolate festival (it happens right after the wine festival). If you have a sweet tooth (like me) you can't miss this one!
christmas festivals budapest December is a good time to be in Budapest for festivals. The Danube Chamber Orchestra has a special concert program for Christmas Day at 8pm on December 25. Also, between November 6 and December 18, the Main Square of Óbuda will host festive programs like concerts, an ice rink and puppet shows on the four weekends of Advent, all free of charge.