Administrative Assistant Day 2012 falls on Wednesday, April 25, 2011. If one day isn't enough time for you to celebrate, the entire week is known as Administrative Professionals Week (formerly known as Secretary's Week).
According to the infallible Wikipedia, the National Secretaries Association, now known as the International Association of Administrative Professionals (IAAP) created the unofficial holiday in 1952 to recognize the work of secretaries, administrative assistants, receptionists, and other administrative support professionals. You may also know them as "Executive Admins" or "Office Managers". This job has more aliases than Sean Combs.
The International Association of Administrative Professionals has actually trademarked the term "Administrative Professionals Day", although people continue to call it whatever they want. Despite the push for the name change, the top Google searches for this holiday are (in order) secretary's day, administrative professionals day, administrative assistant day, professional administrative day.
Typical gifts for Secretary's Day include cards, pins, flowers, gift certificates, lunch, and gift baskets. The IAAP suggests that employers support the holiday by providing training opportunities for their administrative staff through continuing education, self-study materials, or seminars.