<apex:selectList id="accts" value="{!myObject.Report__c}" title="Report">
    <apex:selectOptions value="{!reports}"></apex:selectOptions>
</apex:selectList>

public List<selectOptions> getReports()
{
  List<selectOption> options = new List<selectOption>():
  folder[] ff = [select id from folder where developername = 'My_Reports_Folder'];

  id fid = (ff.isEmpty()) ? null : ff[0].id;

  report[] rpts = [select id, name from report where ownerid = : fid and ownerid != null order by name];

  for (int i=0; i<rpts.length; i++) {
    options.add(new selectOption(rpts[i].id, rpts[i].name));
  }
  return options;
}