Bars! Squeeze them! stretch them! They're fun (as well as being very small, in terms of file size)!
The two attributes to remember regarding bars are WIDTH and HEIGHT. This collection is standard at 400 pixels wide and 8 pixels high, but you can easily make them half again as long (600) or as fat (12) without apparent loss. The most important point is playing with the size till you achieve a pleasing appearance.
Here are the first nine. Right click on any or all of them to save copies.