This site offers for download consolidated versions of important planning documents such as the Use Classes Order and General Development Order.
Whereas the government sites offer consolidated primary legislation, they do not do so for secondary legislation which can make it hard to find out what the current position is (if you don't have easy access to a planning encyclopaedia). We can't vouch for the accuracy of the consolidation but it has all the signs of being produced by a true planning geek who would take great care in their work.
6th June 2014
Note that this is now requires payment if you want to get the full versions of things like the full Permitted Development Rights document.