While I now use Nitto NT-01s as my dedicated track tires, I used to drive on Dunlop Direzza Sport Z1 Star Spec for autocrossing and track. They are by far the best non R-compound tires I have own. They are phenomenal.
The arrival of a replacement tire from Dunlop that's allegedly even better is pretty exciting.
OneHotLap.com has an article about the new Dunlop Direzza ZII Star Spec. Check it out!