#s 3-6 are all so close I could put these in any random order and it would be just as good. #1 and #2 are the only definites in my mind, and then 3-6 is superior to 7, 8, and 9 which I'd be pretty firm on concerning the order. And then there's... everything else, which is still good, but not as good as those first 9.
There haven't been too many more than 10 NIN albums, but I would order them a bit differently. My personal ordering:
1. The Fragile (best album ever recorded by any artist bar none)
2. The Downward Spiral
3. With Teeth
4. Still
5. Pretty Hate Machine
6. Broken
7. And All That Could Have Been (best live album ever)
8. Year Zero
9. The Slip
10. Further Down the Spiral
Not a huge fan of either Ghosts nor Year Zero Remixed... though... the Great Destroyer remix is great. Better than the original studio album version.