Must haves? So many to choose from! You already got the Gayle Bradley, which is a top pick. Beautiful knife.
I'm fairly new to the Spydie addiction (last May), and I've found 32 must haves, so far.
But, if I dare make some suggestions:
Sage 1 & Sage 2 are about as ideal EDC as you can get.
Manix 2 series - robust, ergonomic, rock-solid
Military - the flagship.... gotta have at least one.
Paramilitary 2 - hottest knife at the moment. Everyone wants one.
Lum Chinese (Nishijin Carbon Fiber) - just a gorgeous knife. The CF is unsurpassed.
That's all I'll say for now... gotta go.