P'raps I'm not imaginative enough, but I'm looking at most of these and all I can think is how wildly impractical they are.
Levite's suggestion of the claymore appeals to my heritage, but much as it pains me to say it I suspect I'm simply not big enough to use such a weapon effectively. As such, I'd be more likely to choose something like this, had I the necessity and training:
Simple, elegant and effective.