Correct Date time for salesforce webservice

Correct Date time used for salesforce webservice to insert lead , Live sample C# Asp.net

SQL-SERVER:- SELECT CONVERT(VARCHAR(23), GETDATE(), 126)

C# Code:- DateTime.Now.ToString("yyyy-MM-ddThh:mm:ss-00:00"); 

Hardcoded:- 2008-11-21T04:37:14-05:00