To convert the current machine date and time to a varchar in the format YYYY-MM-DDThh:mm:ss[+|-]hh:mm in T-SQL, you can use the following code:
select convert(varchar(100), cast(sysdatetimeoffset() as datetimeoffset(0)), 126)
Result (in Amsterdam in Summer time)
2012-08-13T15:23:09+02:00