Get the Full limited slip option. As a baseline set your initial to 5. your accel to 30, and your decel to 15. Then adjust, keeping your "accel" at about twice your "decel" value. This is For FR cars only. 4WD is more complicated. For FF cars just buy the one way limited slip.
For cars like the TVR Speed 12, the MR-2 race car, and MR-2 turbo (fully tweaked). Drop the 50,000cr on the TCM and set it around 51 and play with it until you can hang the tail out as much as you want to without spinning. Hope this helps. Oh yeah, in GT2 you can make all your setting for a car go back to factory settings by pressing the "select" button while in each screen for set-up. For example, if you have messed with the original gear ratios and want to just go back to the default setting press the "select" button and the ratios will go back to stock.