Автор: http://www.swissdelphicenter.ch

// This code works also with a TListBox 


var
   Bitmap1, Bitmap2, Bitmap3, Bitmap4: TBitmap;

 procedure TForm1.FormCreate(Sender: TObject);
 begin
   ComboBox1.Style := csOwnerDrawVariable;

   //Set height of one item 
  ComboBox1.ItemHeight := 20;

   //load all bitmaps 

  Bitmap1 := TBitmap.Create;
   Bitmap1.LoadFromFile('chem16.bmp');

   Bitmap2 := TBitmap.Create;
   Bitmap2.LoadFromFile('chip16.bmp');

   Bitmap3 := TBitmap.Create;
   Bitmap3.LoadFromFile('factry16.bmp');

   Bitmap4 := TBitmap.Create;
   Bitmap4.LoadFromFile('skylin16.bmp');

   //assign bitmaps with item objects - caption of the items: Bitmap 1 - Bitmap 4 

  ComboBox1.Items.AddObject('Bitmap 1', Bitmap1);
   ComboBox1.Items.AddObject('Bitmap 2', Bitmap2);
   ComboBox1.Items.AddObject('Bitmap 3', Bitmap3);
   ComboBox1.Items.AddObject('Bitmap 4', Bitmap4);
 end;

 procedure TForm1.ComboBox1DrawItem(Control: TWinControl; Index: Integer;
   Rect: TRect; State: TOwnerDrawState);
 var
   Bitmap: TBitmap;
   Offset: Integer;
 begin
   offset := 0;
   with ComboBox1.Canvas do
   begin
     FillRect(Rect);
     Bitmap := TBitmap(ComboBox1.Items.Objects[Index]);
     if Bitmap <> nil then
     begin
       //copy bitmap to combobox coordinate 
      BrushCopy(Bounds(Rect.Left + 2, Rect.Top + 2, Bitmap.Width,
         Bitmap.Height), Bitmap, Bounds(0, 0, Bitmap.Width,
         Bitmap.Height), clred);
       Offset := Bitmap.Width + 8;
     end;
     //Set a caption to each item 
    TextOut(Rect.Left + Offset, Rect.Top, Combobox1.Items[Index]);
   end;
 end;

 procedure TForm1.FormClose(Sender: TObject; var Action: TCloseAction);
 begin
   //free all bitmap objects 
  bitmap1.Free;
   bitmap2.Free;
   bitmap3.Free;
   bitmap4.Free;
 end;