The Gerber River Guide Knife is my personal favorite. The knife is discontinued, but you can still buy it for $21 ($65 orig):
River Guide II by Gerber : Diving and Marine Knives
I have had one of these for the last 7 years, the rubber grip is super positive even with cold hands and the finger hole makes your grip even more bomb proof. Like True I secure the knife in a couple of ways, I use thin braided cord to secure the sheath to my vest. And I use 1/4" shock cord tied into the knife's lanyard hole with a loop on the top that goes over the top of the sheath. That makes it easy to pop the shock cord off and get to the knife quickly. The River Guide Knife is far from sexy looking, but it is super functional.