I found this really useful little assembly / code when looking for a simple, free way to convert a DataSet to Excel - couldn't be easier, just one line of code required for the conversion, here's the line I'm using:

DataSetToExcel.Convert(ReportsDAL.GetSummaryStats(10, Page.FromDate,Page.UntilDate,Page.MailClientId,0,Page.MailAppId,( int)Page.MailJobStatus),Response);