Your best mod? Worst mod?

I'm all about beefin' stuff up, too. In order of maximum effect:

1) Subframe connectors - felt like a new car after that.
2) Rear suspension (Caltracs/SS Springs/8.75) - Rear is stable and solid. Car seems to beg for punishment.
3) New sway bars (F&R) - Rear suspension punishment entails few surprises.
3) Steer 'n Gear Steering Box. - No substitute for good steering.

No bad mods, yet.