The Turbo Sliding Clutch series is very good. I recommend using the OT-FR56 black 4 shoe clutch or the OT-FR52 black 2 shoe clutch. You can also mix the white shoes with either one, which I have done with very good results. The stock springs work fine, and if you need more punch, try the stiffer springs. When using the 4 shoe setup (OT-FR56) I normally use the stiff springs in the thinner shoes.
The Vario clutch is also good from what I have heard. I have not yet tried one, but a buddy ran one in his DM-1 (on road rally car based on buggy) and he said it was very good.
The new Quattro clutch is also available now; similar to the Vario clutch clutch but with 4 shoes instead of 3, and 2 tension settings (#2 and #3) instead of 3 settings.