As of right now, sdHolidays is the most functional, in terms of ease of use and number of holidays and custom events, holiday managing application in the App Store. Additionally, it is at an extremely low price of $.99!
sdHolidays gives you the dates and a "days until" counter for over 20 major and minor holidays as well as the option to enter your own important dates such as birthdays, anniversaries, etc. It's great for making schedules, planning vacations, and keeping track of important personal days. Dates for holidays are included for each year through 2018 and FREE updates will be provided at least every year.
Not to sound rude or anything, but how many more counter apps do we need to suffer through! I'll give you credit, yours is a more complete app rather than the bulk of the litter which are specific to one holiday.