Visio and Site Template for Workflow
Stephen has posted a site template and visio diagram that goes with the wonderful 14 screen casts that outline a pretty well rounded scenario for starting workflow development (with SharePoint Designer). Again if you are new to workflow, or SharePoint Designer I would highly recommend viewing these screencasts. (Screencast can be found here: http://office.microsoft.com/en-us/sharepointdesigner/HA102564171033.aspx)
The Visio also provides a perfect example of how complex a simple approval workflow actually is when drawn out with a bit of detail. Even if you are experienced with Designer and Workflows I recommend viewing the Visio file to make sure you see a good example of the detail necessary (personally recommended) for documenting a workflow.
Or Download the Diagram and Site Template (http://blogs.msdn.com/sharepointdesigner/attachment/9378075.ashx)
I have already posted about how terrific I think the screencasts are for those who are starting out (http://sharepointkb.wordpress.com/2008/08/25/new-to-workflows-document-reviewapproval-example/) and figured I should also reference the new announcement on the SharePoint Designer blog for anyone interested or starting out with Workflows.
Hope this helps,