Using WHERE clause with BETWEEN and null date parameters

How About:

DateCreated BETWEEN COALESCE(@DateFrom, DateCreated) AND COALESCE(@DateTo, DateCreated)

Just need some extra criteria to handle when one or the other is NULL:

AND (
    (DateCreated >= @DateFrom and DateCreated < DATEADD(day,1,@DateTo)) 
 OR (@DateFrom IS NULL AND @DateTo IS NULL)
 OR (@DateFrom IS NULL AND DateCreated < DATEADD(day,1,@DateTo))
 OR (@DateTo IS NULL AND DateCreated >= @DateFrom)
    )

Edit: Giorgi's approach was simpler, here it is adapted for use with DATETIME:

AND (       (DateCreated >= @DateFrom OR @DateFrom IS NULL) 
        AND (DateCreated < DATEADD(day,1,@DateTo) OR @DateTo IS NULL)
    )

The issue with BETWEEN or <= when using a DATE variable against a DATETIME field, is that any time after midnight on the last day will be excluded.

'2015-02-11 13:07:56.017' is greater than '2015-02-11' Rather than casting your field as DATE for comparison, it's better for performance to add a day to your variable and change from <= to <.

Try this:

WHERE ((DateCreated >= @DateFrom OR @DateFrom IS NULL) AND (DateCreated =< @DateTo OR @DateTo IS NULL))