The date on your annual report should refer to the time period that the text covers. Most nonprofits issue their 2007 Annual Report in 2008, because they are talking about the previous year's accomplishments. If your fiscal year overlaps two calendar years, include both years in your title, e.g., 2007-2008 Annual Report.
The exception to the rule is when you issue a "Progress Report" that summarizes recent achievements without assigning them to a standard timeframe. In that case, it is acceptable to use the year the report was issued in, e.g., 2008 Progress Report.