SQL Server Group by Count of DateTime Per Hour?

How about this? Assuming SQL Server 2008:

SELECT CAST(StartDate as date) AS ForDate,
       DATEPART(hour,StartDate) AS OnHour,
       COUNT(*) AS Totals
FROM #Events
GROUP BY CAST(StartDate as date),
       DATEPART(hour,StartDate)

For pre-2008:

SELECT DATEADD(day,datediff(day,0,StartDate),0)   AS ForDate,
       DATEPART(hour,StartDate) AS OnHour,
       COUNT(*) AS Totals
FROM #Events
GROUP BY CAST(StartDate as date),
       DATEPART(hour,StartDate)

This results in :

ForDate                 | OnHour | Totals
-----------------------------------------
2011-08-09 00:00:00.000     12       3

Alternatively, just GROUP BY the hour and day:

SELECT  CAST(Startdate as DATE) as 'StartDate', 
        CAST(DATEPART(Hour, StartDate) as varchar) + ':00' as 'Hour', 
        COUNT(*) as 'Ct'
FROM #Events
GROUP BY CAST(Startdate as DATE), DATEPART(Hour, StartDate)
ORDER BY CAST(Startdate as DATE) ASC

output:

StartDate   Hour    Ct
2007-01-01  0:00    3
2007-01-02  5:00    2
2007-01-03  4:00    1
2007-01-07  3:00    1

I found this somewhere else. I like this answer!

SELECT [Hourly], COUNT(*) as [Count]
  FROM 
 (SELECT dateadd(hh, datediff(hh, '20010101', [date_created]), '20010101') as [Hourly]
    FROM table) idat
 GROUP BY [Hourly]