Concatenating Date and Time in T-SQL

Sometimes you just want to concatenate the date section from a DateTime and the time section from another DateTime.  These could even be the new SQL Server Date or Time data types.  The easiest way I've found to do this is by combining DATEPART with DATEADD.  You get rid of the parts of each DateTime that you don't want and then add based on the lowest common denominator this being millisecond.

'ProcessedDate' = DATEADD(ms, DATEDIFF(ms, 0, [ProcessingTime]), DATEADD(dd, 0, DATEDIFF(dd, 0, [ProcessingDate])))