OSX AppStore Avoid updating certain apps
If you click the More button at the bottom of the listed item, then right click after it has expanded, you should get a 'Hide Update' button - but it doesn't work for all apps.

Tested today with 


Camera Raw 5.0.7 - Hide Update button
OS X Update 10.9.5 - Hide Update button
Xcode 6.0.1 - no Hide Update button