Ephi (along with some help from the other RTB chums) add nice new features that really expand Blockland and add allot more ease to use.
Trader is really good at interactive stuff, and making systems that have universal uses throughout most builds.
Kaje is the best Blockland modeler out there. Take him out of the picture and most of my favorite vehicles go with him (the only one staying being the magic carpet, I just like how it handles.)
Though my award my favorite blockland modder goes to Nit, because while he may not make many public things, I have spent hours upon hours having a blast on his servers.
Also a runner up award goes to Mr.Wallet for making a super great game mod that gets many people building, often having to end the game because the build got too big to handle.