For a tri-tip that's crusty on the outside and pink in the middle, try this method:
On a charcoal grill set up for indirect-heat cooking, place the meat directly over one bank of hot coals (using tongs). On a gas grill, do the same over high flame. Sear the meat for five to seven minutes on each side, but watch for flare-ups.
Move the tri-tip to the center of the charcoal grill. On a gas grill, turn down the heat and move it off the direct flame.
Cook it uncovered (Santa Maria-style) or covered for 25-30 minutes or so, depending on size. Turn it a few times.
When the internal temperature reaches 120 degrees in the center of the roast, remove it from the charcoal grill, tent with aluminum foil and let it stand for 15-20 minutes. On a gas grill, turn off the gas and let the tri-tip sit on the grill, with the grill hood down, for the same amount of time. The internal temperature will reach 130 to 135 degrees in that time.
Slice across the grain, garnish with sesame seeds or cilantro, and serve with condiments.