Calculate the last day of the prior quarter

Question

What\'s the most efficient way to calculate the last day of the prior quarter?

Example: given the date 11/19/2008, I want to return 9/30/2008.

Platform is S

Answer 1

If @Date has the date in question

Select DateAdd(day, -1, dateadd(qq, DateDiff(qq, 0, @Date), 0)) 

EDIT: Thanks to @strEagle below, simpler still is:

Select dateadd(qq, DateDiff(qq, 0, @Date), -1)