Stainless Steel lines, I called them braided. We had some sets made for the guys who race their E30's down here, less than $300 NZD per set, then fit them. Not a major job and one I'd recommend if you hammer your brakes, but again, if you have good firm brake lines now, you will not notice a performance increase until you get to the track and do 3 HOT laps and would normally start to experience brake fade. We also need to have them approved by the ministry of transport, so it requires and engineering certificate to have them legal for road use. Don't know how the US looks at it.
Better tyres will bring about a better stopping performance than Braided (SS) lines will for normal driving conditions.