Since our year end is December 31st, I'm currently working with our Accountant to file our 990 for 2006—which is due June 15th. It is rather fitting that while I was attending the West Coast Nonprofit Data Conference [1] over the weekend, I learned about the Urban Institute's Electronic Filing Service for Nonprofits [2].
There are many great things about this service that allows nonprofits to file their 990, 990-PF, or 990-EZ online, however I really like the fact that nonprofits don't have to re-enter their 990 information, the service automatically inputs data from previous years 990 filings!
Just a small bit of advice—Make sure you have someone in house or hire an outside consultant who knows how to fill out a 990 form!