Thanks all, for the great suggestions. Based on the advice I have so far, it seems like my original thoughts about buying an SnG or Sebenza were not too bad.
I just wanted to answer some questions that have come up:
mschwoeb: I'm not a "steel snob", so any type of steel that would be put into a $400 knife is fine. I've had good experiences with S30V and 154CM, so those would work for me. As you can see by the knives I suggested, I'm open to almost anything. I think that, at this price range, my selection comes down to personal taste more than anything; you'd probably be hard pressed to find a bad knife in this price range.
ColoradoDave: As I mentioned in my post, I've been collecting for 20 or so years, so I have a feel for the price range, at the very least. I know there are many good tactical folders in the $350 - $450 range, so I just used $400 as a starting price. The problem with continuing to save is twofold: first, I'm a gadget junkie. I know if I hold on to this money for too long, I'm going to piss it away, little by little, and end up with 3 or 4 $100 toys instead of one nice knife. Secondly, if I spend much more than $400, I know I'm just going to put the knife in the display case, because I'd be afraid to use such an expensive knife. I'm really intent on buying a user, and really using it.
Right now I'm leaning towards the Large Classic Sebenza, but if a nice SnG comes up for sale...
I'm curious: I mentioned a Crawford KFF and Tighe folder, but no one has said anything about those. Anyone have a negative experience with either maker, or are they just "off the radar" right now?