From what I see on OCUK, it appears they are mostly the same design and build (they do have differences) but the size and modularity appears to change. I am looking at buying the 410 for my next build. Only thing I'm not sure on is if it will house a GTX 780 which I'm pretty sure it will but I will ask OCUK before I buy if it does.
NOTE: There are articles about the white editions of their cases of the paint flaking off, so stay away from them.. Supposedly...
The 820 is meant to be huge...
Full NZXT Product range:
http://www.overclockers.co.uk/productlist.php?groupid=2362&catid=35
NZXT Phantom 410 I am thinking about getting:
http://www.overclockers.co.uk/showproduct.php?prodid=CA-080-NX
NZXT Phantom 530
http://www.overclockers.co.uk/showproduct.php?prodid=CA-128-NX&groupid=2362&catid=35
NZXT Phantom 630
http://www.overclockers.co.uk/showproduct.php?prodid=CA-122-NX&groupid=2362&catid=35
NZXT Phantom 820
http://www.overclockers.co.uk/showproduct.php?prodid=CA-112-NX&groupid=2362&catid=35