Copper plugs or platinums. Platinums because thats what Toyota themselves suggested with much $$$ dumped into research, copper because of the properties. Copper is one of the best performing spark plugs (ask resident MkIII god Dr. Jonez...Autolites for him) and also the cheapest. The only "downside" is that you have to replace them far more often. Whoop de do, I paid no more than $8 for all 6 of mine and DOHC Inline 6s are some of the easiest cars to change spark plugs on out there.
Lots of people complain that theres too much on the engine and you have to move it all to change plugs, but I've changed them moving only the coil pack and the 3000 pipe...no throttle cable or anything else needs to be moved, plug the problem is solved with FFIM