This looks complex but will use your index.
where CreatedDate between dateadd(dd, datediff(dd,0,Getdate()),0) --midnight TODAY
and dateAdd(ss,-1,dateAdd(dd,1,dateadd(dd, datediff(dd,0,Getdate()),0))) --23:59:59 TODAY
HTH
Dave J
Edit: Oops! I see w.lengenfelder posted this already! :w00t: