One of the announcements from Wednesday's Apple event (re-watch it over and over again!) was that in November the iPad is getting the same update as the iPhone is getting next week, iOS 4.2.
Here's a page detailing the updates that will be new to iPad owners, including multi-tasking, printing and Airplay ("Wirelessly stream videos, music, and photos from iPad to the new Apple TV, and stream music to AirPlay speakers or receivers, including AirPort Express.")
The iOS 4.2 update will be a free update.