T-SQL: Get first day of the current month

You get a lot of people asking to find out first/last days of months based upon a certain date. Essentially, you can work out nearly anything you want just by getting day 1 of your current month and then using the date functions.

Although this is posted in hundreds of places on the web, for my own sanity as much as anything i'm going to post it here too.

DECLARE @TestDate DATE = '20110417';

SELECT DATEADD(M, DATEDIFF(M, 0, @TestDate), 0) AS NewDate;

-- NewDate
-- 2011-04-01 00:00:00.000