As has been said, the best first mod for an automatic is a high-stall Torque Converter. This enables the engine to spool up into it's power band more quickly so that the car launches quicker and generally stays where the power is being made, not waiting to rev up to it.
So I had a FTI/RX 3200 Billet Torque Converter installed last week. The only other recent mod was the JBA High-Flow Catted Midpipes, which gained me about a tenth of a second on the ET in the 1/4 mile and about 2 mph on the top end.
The new torque converter gained me 0.43 seconds, including a 1.713 sixty-foot. So the car really launches hard now and the Nitto 555R drag radials are loving it - no spin at all.
My new best time is:
1/4: 12.413 @ 110.18 mph
1/8: 7.965 @ 87.52 mph
sixty: 1.713
I'm very pleased with the results, and there's still more in the car as is.