If we are talking brands, Kershaw (150+ now), and more enthusiastically now, ZTs (40 now and growing).
If we are talking versions of a model, Skyline (have almost all the versions, though I am thinking of selling them off to fund ZT purchases), 0801 (had 4 versions, now down to 2), 0560BW/0561, Leek (down to 4 now), Chive (have almost all of the versions), Blur (down to 4 now), Starkey Ridge, Talon, Hawk, Wild Wild Turkey, plus some others that I'm sure I'm missing.
The specific models that I have (or did have) multiples of are the old Hawk G10, Wild Wild Turkey G10, Wild Wild Turkey Ti, and ZT0780. I sold my user 0780 a while back, and I have regretted it ever since. Still have a perfect example in the collection, though.