I would like to generate a report of all candidates where a timesheet has been submitted showing the value - which report will show this information?

This really depends on the status of the timesheet(s). If you are interested in timesheets that have not yet been processed (so not billed/paid or timesheets that are mid-process) the best report is the Unprocessed Timesheet Report within the Reports menu.  The report can be exported to excel as shown:

The General Reporting article contains a link to our Reports Guide which you may also find useful:

General reporting guide