How do I stop Apple from offering me iTunes 11 as a software download in OS X
The methods differ based on whether you are using OS X Mountain Lion, or an earlier edition.

For OS X Mountain Lion (where updates are now merged with the Mac App Store):


Refer to HT2357 How can you ignore a software update in Mountain Lion? &ndash; Apple Support Communities. Quoting the accepted solution from DickVH: 



  For the software update you would like to hide - make sure the full
  description of the update is shown - click "More..." if needed to show
  the full description
  
  Right click on the update window.  Select "Hide update"
  
  This will hide the update and it will not show in the App Store
  Updates Window or counted on the dock icon. [...]
  
  [emphasis above is mine]


For OS X Lion and earlier:


Refer to OS X: How to ignore a Software Update &ndash; Apple Support. Quote:



  How to ignore an update
    [Mac OS X 10.3, Mac OS X 10.4, Mac OS X 10.5, Mac OS X 10.6, OS X Lion]
  
  
  Choose Software Update from the Apple menu.
  Click Show Details when prompted.
  Click to select the name of the update you wish to ignore.
  Choose Ignore Update… from the Update menu. A confirmation dialog appears that states, "Are you sure you want to
  remove the update (name of update) from the list? You will no longer
  be notified of new versions of this update. To see this update again,
  choose Software Update > Reset Ignored Updates."
  Click OK.