Aperture has a few different options for the order that images appear in the Browser pane, but some of them aren't immediately visible.

The first point of call is the drop-down menu at the top left of the Browser pane, which will let you order the images by:
Image Date
Rating
Version Name
File name
Keywords
File Size
Orientation
Pixel Size

The other option listed is 'Custom', which is what will appear if you manually drag images into a specific order. Note that you can then swap back-and-forth between custom and one of the other orders, and Aperture will remember the custom order that you used.

What if you want to order the Versions by some other criteria, such as ISO or shutter speed? List View and Metadata Views are your friend here. If you go into List View, you can change the display order simply by clicking on the top of the relevant column. Click again to reverse the order. If the metadata tag you are after doesn't appear, hit Command-J to bring up the Metadata preferences pane, and then choose an appropriate Metadata View to use as the List View columns.

Ah, but what happens if you swap out of List View? The order stays the same, until you manually change it. So you can set up almost any automatic order, by swapping into List View and back.

Ian