Here's the one I've used...

SELECT TimeSheets.EmployeeID, Month(WorkDate) as MonthPay , YEAR(WorkDate) AS YearPay,
   SUM(TimeSheets.HoursWorked * WorkerRates.HourlyRate)  AS LaborDollars
        FROM TimeSheets
              JOIN WorkerRates ON WorkerRates.EmployeeID = TimeSheets.EmployeeID 

                  WHERE WorkerRates.RateEffectiveDate = 
                        (SELECT MAX(RateEffectiveDate) FROM WorkerRates RatesTemp
                                      WHERE RateEffectiveDate <= WorkDate AND 
                                                     RateAddedDate <= WorkDate AND 
                                                   RatesTemp.EmployeeID = TimeSheets.EmployeeID)
    GROUP BY TimeSheets.EmployeeID, Month(WorkDate),YEAR(WorkDate)

Obviously, you could use a CTE as well.

Our execution plans are different....yours is interesting....obvoiusly, more than one way to do it.

Later tonight I'll try to post the execution plans.

Thanks for participating...