System Preferences - International
Go to the 'Formats' tab and under 'Dates' click on the 'Customize' button
In the 'Show:' box start out in the 'Medium' or 'Long' formats, whichever comes the closest to what you want. You can drag other items into it, to make it like you want it. Once you have the date the way you would like it to appear, Highlight it, copy it and then click on 'Cancel'.
Now click the 'Customize' button under 'Time'. Next to 'Show:', select 'Medium'. Paste what you just copied above into the box wherever you want it to appear. Click OK.
Check out the appearance on the 'Menu Bar'. You may have to go back in and adjust the spaces or something else to get it just the way you want.