I put 3.46 gears in. You could go 3.7's or 3.9's if you plan to take it to the track a lot, but i think the 3.46 are the best all round gears, especially for an auto. I sit on 2,100 RPM at 100 kph which is barely noticeable difference to the 1,800 RPM 3.08 gears sit on. By going to 3.46 gear you get equivalent to an extra 10% more power at the rear wheels, which coupled with a LSD makes for some good fun
I bought my gears from
ebay however the company i bought them from have a website too - see
Diff Technics.
You will need to get the speedo recalibrated, which cost me $55 (i think) - had it done later on when i got the car serviced - just meant in the mean time i could sit on 110 on the speedo coz it was really 100 (just looks faster

)
Cheers,
Matt
BTW. the HSV LSD for the VT had 3.46 gears in it (or 3.45 in the VS i think)