Important date queries in SQL Server 2005

Query to fetch current date in '2010-02-23 00:00:00.000' format
SELECT DATEADD(d, DATEDIFF(d, 0, GETDATE())+0, 0)
OR
SELECT DATEADD(d, 0, DATEDIFF(d, 0, GETDATE()) )

Query to fetch current date in '2010-02-23 11:59:59.000' format
SELECT DATEADD(ss, +43199, DATEADD(d, DATEDIFF(d, 0, GETDATE())+0, 0))
OR
SELECT DATEADD(s, -1, DATEADD(d, 0, DATEDIFF(d, 0, GETDATE()) ) + 1)

Few days back I had a requirement that, I have to find out start date of the week, considering Monday as first day of the week. I have search on the internet for available solution and found the following query,
SELECT DATEADD(wk, DATEDIFF(wk, 0, GETDATE()), 0)
Output is : 2010-10-04 00:00:00.000

Soon I have noticed a problem with above query that instead of using GETDATE() if I pass any date when the day is Sunday, for eg. I pass '2010-10-03' then it should return me ‘2010-09-27’ but it is returning me '2010-10-04'. With the following query, you will notice that output  is not meeting our requirement
SELECT DATEADD(wk, DATEDIFF(wk, 0, '2010-10-03'), 0)
Output is : 2010-10-04 00:00:00.000

So, I have used the following query which will help to solve above mentioned problem
SELECT (CAST('2010-01-05' AS DATETIME) - DATEPART(dw, CAST('2010-01-05' AS DATETIME)-1)) +1
Output is : 2010-09-27 00:00:00.000